[ { "text": "A Time-Orbiting Potential Trap for Bose-Einstein Condensate\n Interferometry: We describe a novel atom trap for Bose-Einstein condensates of 87Rb to be\nused in atom interferometry experiments. The trap is based on a time-orbiting\npotential waveguide. It supports the atoms against gravity while providing weak\nconfinement to minimize interaction effects. We observe harmonic oscillation\nfrequencies omega_x, omega_y, omega_z as low as 2 pi times (6.0,1.2,3.3) Hz. Up\nto 2 times 10^4 condensate atoms have been loaded into the trap, at estimated\ntemperatures as low as 850 pK. We anticipate that interferometer measurement\ntimes of 1 s or more should be achievable in this device.", "category": "cond-mat_other" }, { "text": "Diamagnetism and the dispersion of the magnetic permeability: It is well known that the usual Kramers--Kronig relations for the relative\npermeability function $\\mu(\\omega)$ are not compatible with diamagnetism\n($\\mu(0)<1$) and a positive imaginary part ($\\text{Im}\\,\\mu(\\omega)>0$ for\n$\\omega>0$). We demonstrate that a certain physical meaning can be attributed\nto $\\mu$ for all frequencies, and that in the presence of spatial dispersion,\n$\\mu$ does not necessarily tend to 1 for high frequencies $\\omega$ and fixed\nwavenumber $\\mathbf k$. Taking the asymptotic behavior into account,\ndiamagnetism can be compatible with Kramers--Kronig relations even if the\nimaginary part of the permeability is positive. We provide several examples of\ndiamagnetic media and metamaterials for which $\\mu(\\omega,\\mathbf k)\\not\\to 1$\nas $\\omega\\to\\infty$.", "category": "cond-mat_other" }, { "text": "Influence of topography and Co domain walls on the magnetization\n reversal of the FeNi layer in FeNi/Al$\\_2$O$\\_3$/Co magnetic tunnel junctions: We have studied the magnetization reversal dynamics of FeNi/Al$\\_2$O$\\_3$/Co\nmagnetic tunnel junctions deposited on step-bunched Si substrates using\nmagneto-optical Kerr effect and time-resolved x-ray photoelectron emission\nmicroscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM).\nDifferent reversal mechanisms have been found depending on the substrate miscut\nangle. Larger terraces (smaller miscut angles) lead to a higher nucleation\ndensity and stronger domain wall pinning. The width of domain walls with\nrespect to the size of the terraces seems to play an important role in the\nreversal. We used the element selectivity of XMCD-PEEM to reveal the strong\ninfluence of the stray field of domain walls in the hard magnetic layer on the\nmagnetic switching of the soft magnetic layer.", "category": "cond-mat_other" }, { "text": "Spin-Exchange Interaction in ZnO-based Quantum Wells: Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit\nunprecedented tunability of the short-range spin exchange interaction. In the\ncontext of large exciton binding energies and electron-hole exchange\ninteraction in ZnO, this tunability results from the competition between\nquantum confinement and giant quantum confined Stark effect. By using\ntime-resolved photoluminescence we identify, for well widths under 3 nm, the\nredistribution of oscillator strengths between the A and B excitonic\ntransitions, due to the enhancement of the exchange interaction. Conversely,\nfor wider wells, the redistribution is cancelled by the dominant effect of\ninternal electric fields, which dramatically reduce the exchange energy.", "category": "cond-mat_other" }, { "text": "A basis-set based Fortran program to solve the Gross-Pitaevskii Equation\n for dilute Bose gases in harmonic and anharmonic traps: Inhomogeneous boson systems, such as the dilute gases of integral spin atoms\nin low-temperature magnetic traps, are believed to be well described by the\nGross-Pitaevskii equation (GPE). GPE is a nonlinear Schroedinger equation which\ndescribes the order parameter of such systems at the mean field level. In the\npresent work, we describe a Fortran 90 computer program developed by us, which\nsolves the GPE using a basis set expansion technique. In this technique, the\ncondensate wave function (order parameter) is expanded in terms of the\nsolutions of the simple-harmonic oscillator (SHO) characterizing the atomic\ntrap. Additionally, the same approach is also used to solve the problems in\nwhich the trap is weakly anharmonic, and the anharmonic potential can be\nexpressed as a polynomial in the position operators x, y, and z. The resulting\neigenvalue problem is solved iteratively using either the self-consistent-field\n(SCF) approach, or the imaginary time steepest-descent (SD) approach. Our\nresults for harmonic traps are also compared with those published by other\nauthors using different numerical approaches, and excellent agreement is\nobtained. GPE is also solved for a few anharmonic potentials, and the influence\nof anharmonicity on the condensate is discussed. Additionally, the notion of\nShannon entropy for the condensate wave function is defined and studied as a\nfunction of the number of particles in the trap. It is demonstrated numerically\nthat the entropy increases with the particle number in a monotonic way.", "category": "cond-mat_other" }, { "text": "Fully three dimensional breather solitons can be created using Feshbach\n resonance: We investigate the stability properties of breather solitons in a\nthree-dimensional Bose-Einstein Condensate with Feshbach Resonance Management\nof the scattering length and con ned only by a one dimensional optical lattice.\nWe compare regions of stability in parameter space obtained from a fully 3D\nanalysis with those from a quasi two-dimensional treatment. For moderate con\nnement we discover a new island of stability in the 3D case, not present in the\nquasi 2D treatment. Stable solutions from this region have nontrivial dynamics\nin the lattice direction, hence they describe fully 3D breather solitons. We\ndemonstrate these solutions in direct numerical simulations and outline a\npossible way of creating robust 3D solitons in experiments in a Bose Einstein\nCondensate in a one-dimensional lattice. We point other possible applications.", "category": "cond-mat_other" }, { "text": "Dynamical Instability of a Doubly Quantized Vortex in a Bose-Einstein\n condensate: Doubly quantized vortices were topologically imprinted in $|F=1>$ $^{23}$Na\ncondensates, and their time evolution was observed using a tomographic imaging\ntechnique. The decay into two singly quantized vortices was characterized and\nattributed to dynamical instability. The time scale of the splitting process\nwas found to be longer at higher atom density.", "category": "cond-mat_other" }, { "text": "Rabi switch of condensate wavefunctions in a multicomponent Bose gas: Using a time-dependent linear (Rabi) coupling between the components of a\nweakly interacting multicomponent Bose-Einstein condensate (BEC), we propose a\nprotocol for transferring the wavefunction of one component to the other. This\n\"Rabi switch\" can be generated in a binary BEC mixture by an electromagnetic\nfield between the two components, typically two hyperfine states. When the\nwavefunction to be transfered is - at a given time - a stationary state of the\nmulticomponent Hamiltonian, then, after a time delay (depending on the Rabi\nfrequency), it is possible to have the same wavefunction on the other\ncondensate. The Rabi switch can be used to transfer also moving bright\nmatter-wave solitons, as well as vortices and vortex lattices in\ntwo-dimensional condensates. The efficiency of the proposed switch is shown to\nbe 100% when inter-species and intra-species interaction strengths are equal.\nThe deviations from equal interaction strengths are analyzed within a two-mode\nmodel and the dependence of the efficiency on the interaction strengths and on\nthe presence of external potentials is examined in both 1D and 2D settings.", "category": "cond-mat_other" }, { "text": "Confinement-induced resonances for a two-component ultracold atom gas in\n arbitrary quasi-one-dimensional traps: We solve the two-particle s-wave scattering problem for ultracold atom gases\nconfined in arbitrary quasi-one-dimensional trapping potentials, allowing for\ntwo different atom species. As a consequence, the center-of-mass and relative\ndegrees of freedom do not factorize. We derive bound-state solutions and obtain\nthe general scattering solution, which exhibits several resonances in the 1D\nscattering length induced by the confinement. We apply our formalism to two\nexperimentally relevant cases: (i) interspecies scattering in a two-species\nmixture, and (ii) the two-body problem for a single species in a non-parabolic\ntrap.", "category": "cond-mat_other" }, { "text": "Strong coupling theory for the superfluidity of Bose-Fermi mixtures: We develop a strong-coupling theory for the superfluidity of fermion pairing\nphase in a Bose-Fermi mixture. Dynamical screening, self-energy\nrenormalization, and a pairing gap function are included self-consistently\nwithin the adiabatic limit (i.e., the phonon velocity is much smaller than the\nFermi velocity). An analytical solution for the transition temperature (Tc) is\nderived within reasonable approximations. Using typical parameters of a\n40K-87Rb mixture, we find that the calculated Tc is several times larger than\nthat obtained in the weak coupling theory, and can be up to several percents of\nthe Fermi temperature.", "category": "cond-mat_other" }, { "text": "Coexisting ordinary elasticity and superfluidity in a model of\n defect-free supersolid: We present the mechanics of a model of supersolid in the frame of the\nGross-Pitaevskii equation at $T=0K$ that do not require defects nor vacancies.\nA set of coupled nonlinear partial differential equations plus boundary\nconditions is derived. The mechanical equilibrium is studied under external\nconstrains as steady rotation or external stress. Our model displays a\nparadoxical behavior: the existence of a non classical rotational inertia\nfraction in the limit of small rotation speed and no superflow under small (but\nfinite) stress nor external force. The only matter flow for finite stress is\ndue to plasticity.", "category": "cond-mat_other" }, { "text": "Spin dynamics for bosons in an optical lattice: We study the internal dynamics of bosonic atoms in an optical lattice. Within\nthe regime in which the atomic crystal is a Mott insulator with one atom per\nwell, the atoms behave as localized spins which interact according to some spin\nHamiltonian. The type of Hamiltonian (Heisenberg, Ising), and the sign of\ninteractions may be tuned by changing the properties of the optical lattice, or\napplying external magnetic fields. When, on the other hand, the number of atoms\nper lattice site is unknown, we can still use the bosons to perform general\nquantum computation.", "category": "cond-mat_other" }, { "text": "Extracting spectral density function of a binary composite without\n a-priori assumption: The spectral representation separates the contributions of geometrical\narrangement (topology) and intrinsic constituent properties in a composite. The\naim of paper is to present a numerical algorithm based on the Monte Carlo\nintegration and contrainted-least-squares methods to resolve the spectral\ndensity function for a given system. The numerical method is verified by\ncomparing the results with those of Maxwell-Garnett effective permittivity\nexpression. Later, it is applied to a well-studied rock-and-brine system to\ninstruct its utility. The presented method yields significant microstructural\ninformation in improving our understanding how microstructure influences the\nmacroscopic behaviour of composites without any intricate mathematics.", "category": "cond-mat_other" }, { "text": "STM Studies of TbTe3: Evidence for a fully Incommensurate Charge Density\n Wave: We observe unidirectional charge density wave ordering on the cleaved surface\nof TbTe3 with a Scanning Tunneling Microscope at ~6 K. The modulation\nwave-vector q_{CDW} as determined by Fourier analysis is 0.71 +/- 0.02 * 2\npi/c. (Where c is one edge of the in-plane 3D unit cell.) Images at different\ntip-sample voltages show the unit cell doubling effects of dimerization and the\nlayer below. Our results agree with bulk X-ray measurements, with the addition\nof ~(1/3) * 2 pi/a ordering perpendicular to the CDW. Our analysis indicates\nthat the CDW is incommensurate.", "category": "cond-mat_other" }, { "text": "Energy and Vorticity Spectra in Turbulent Superfluid $^4$He from $T=0$\n to $T_\u03bb$: We discuss the energy and vorticity spectra of turbulent superfluid $^4$He in\nall the temperature range from $T=0$ up to the phase transition \"$\\lambda$\npoint\", $T_\\lambda\\simeq 2.17\\,$K. Contrary to classical developed turbulence\nin which there are only two typical scales, i.e. the energy injection $L$ and\nthe dissipation scales $\\eta$, here the quantization of vorticity introduces\ntwo additional scales, i.e the vortex core radius $a_0$ and the mean vortex\nspacing $\\ell$. We present these spectra for the super- and normal-fluid\ncomponents in the entire range of scales from $L$ to $a_0$ including the\ncross-over scale $\\ell$ where the hydrodynamic eddy-cascade is replaced by the\ncascade of Kelvin waves on individual vortices. At this scale a bottleneck\naccumulation of the energy was found earlier at $T=0$.\n We show that even very small mutual friction dramatically suppresses the\nbottleneck effect due to the dissipation of the Kelvin waves. Using our results\nfor the spectra we estimate the Vinen \"effective viscosity\" $\\nu'$ in the\nentire temperature range and show agreement with numerous experimental\nobservation for $\\nu'(T)$.", "category": "cond-mat_other" }, { "text": "Imaging of s and d partial-wave interference in quantum scattering of\n identical bosonic atoms: We report on the direct imaging of s and d partial-wave interference in cold\ncollisions of atoms. Two ultracold clouds of Rb87 atoms were accelerated by\nmagnetic fields to collide at energies near a d-wave shape resonance. The\nresulting halos of scattered particles were imaged using laser absorption. By\nscanning across the resonance we observed a marked evolution of the scattering\npatterns due to the energy dependent phase shifts for the interfering s and d\nwaves. Since only two partial wave states are involved in the collision process\nthe scattering yield and angular distributions have a simple interpretation in\nterms of a theoretical model.", "category": "cond-mat_other" }, { "text": "Mean-field dynamics of a two-mode Bose-Einstein condensate subject to\n noise and dissipation: We discuss the dynamics of an open two-mode Bose-Hubbard system subject to\nphase noise and particle dissipation. Starting from the full many-body dynamics\ndescribed by a master equation the mean-field limit is derived resulting in an\neffective non-hermitian (discrete) Gross-Pitaevskii equation which has been\nintroduced only phenomenologically up to now. The familiar mean-field phase\nspace structure is substantially altered by the dissipation. Especially the\ncharacter of the fixed points shows an abrupt transition from elliptic or\nhyperbolic to attractiv or repulsive, respectively. This reflects the\nmetastable behaviour of the corresponding many-body system which surprisingly\nalso leads to a significant increase of the purity of the condensate. A\ncomparison of the mean-field approximation to simulations of the full master\nequation using the Monte Carlo wave function method shows an excellent\nagreement for wide parameter ranges.", "category": "cond-mat_other" }, { "text": "Probing Strong Correlations with Light Scattering: the Example of the\n Quantum Ising model: In this paper we calculate the nonlinear susceptibility and the resonant\nRaman cross section for the paramagnetic phase of the ferromagnetic Quantum\nIsing model in one dimension. In this region the spectrum of the Ising model\nhas a gap $m$. The Raman cross section has a strong singularity when the energy\nof the outgoing photon is at the spectral gap $\\omega_{f} \\approx m$ and a\nsquare root threshold when the frequency difference between the incident and\noutgoing photons $\\omega_{i} -\\omega_{f} \\approx 2m$. The latter feature\nreflects the fermionic nature of the Ising model excitations.", "category": "cond-mat_other" }, { "text": "Natural orbits of atomic Cooper pairs in a nonuniform Fermi gas: We examine the basic mode structure of atomic Cooper pairs in an\ninhomogeneous Fermi gas. Based on the properties of Bogoliubov quasi-particle\nvacuum, the single particle density matrix and the anomalous density matrix\nshare the same set of eigenfunctions. These eigenfunctions correspond to\nnatural pairing orbits associated with the BCS ground state. We investigate\nthese orbits for a Fermi gas in a spherical harmonic trap, and construct the\nwave function of a Cooper pair in the form of Schmidt decomposition. The issue\nof spatial quantum entanglement between constituent atoms in a pair is\naddressed.", "category": "cond-mat_other" }, { "text": "Cluster states of Fermions in the single l-shell model: The paper concerns the ground state structure of the partly filled l-shell of\na fermionic gas of atoms of spin s in a spherically symmetric spin independent\ntrap potential. At particle numbers N=n(2s+1), n=1,2,...,2l+1 the basic\nbuilding blocks are clusters consisting of (2s+1) atoms, whose wave functions\nare completely symmetric and antisymmetric in space and spin variables,\nrespectively. The creation operator of a cluster is constructed whose repeated\napplication to the vacuum leads to the multi-cluster state. Ground state energy\nexpressions are derived for the n-cluster states at different l,s values and\ninterpreted in simple terms.", "category": "cond-mat_other" }, { "text": "On the Order Parameter of the Continuous Phase Transition in the\n Classical and Quantum Mechanical limits: The mean field theory is revisited in the classical and quantum mechanical\nlimits. Taking into account the boundary conditions at the phase transition and\nthe third law of the thermodynamics the physical properties of the ordered and\ndisordered phases were reported. The equation for the order parameter predicts\nthe occurrence of a saturation of $\\Psi^2$ = 1 near $\\Theta_S$, the temperature\nbelow the quantum mechanical ground state is reached. The theoretical\npredictions are also compared with high resolution thermal expansion data of\nSrTiO$_{\\text{3}}$ monocrystalline samples and other some previous results. An\nexcellent agreement has been found suggesting a universal behavior of the\ntheoretical model to describe continuous structural phase transitions.", "category": "cond-mat_other" }, { "text": "Reply to Comment on \"Dynamics of the Density of Quantized Vortex-Lines\n in Superfluid Turbulence\": This is a Reply to Nemirovskii Comment [Phys. Rev. B 94, 146501 (2016)] on\nthe Khomenko et al, [Phys.Rev. B v.91, 180504(2016)], in which a new form of\nthe production term in Vinen's equation for the evolution of the vortex-line\ndensity $\\cal L$ in the thermal counterflow of superfluid $^4$He in a channel\nwas suggested. To further substantiate the suggested form which was questioned\nin the Comment, we present a physical explanation for the improvement of the\nclosure suggested in Khomenko et al [Phys.Rev. B v. 91, 180504(2016)] in\ncomparison to the form proposed by Vinen. We also discuss the closure for the\nflux term, which agrees well with the numerical results without any fitting\nparameters.", "category": "cond-mat_other" }, { "text": "Sufficient conditions for two-dimensional localization by arbitrarily\n weak defects in periodic potentials with band gaps: We prove, via an elementary variational method, 1d and 2d localization within\nthe band gaps of a periodic Schrodinger operator for any mostly negative or\nmostly positive defect potential, V, whose depth is not too great compared to\nthe size of the gap. In a similar way, we also prove sufficient conditions for\n1d and 2d localization below the ground state of such an operator. Furthermore,\nwe extend our results to 1d and 2d localization in d dimensions; for example, a\nlinear or planar defect in a 3d crystal. For the case of D-fold degenerate band\nedges, we also give sufficient conditions for localization of up to D states.", "category": "cond-mat_other" }, { "text": "Self-consistent calculation of semiconductor heterojunctions by using\n quantum genetic algorithm: In this study, we have investigated the ground state energy level of\nelectrons in modulation doped GaAs/AlxGa1-xAs heterojunctions. For this\npurpose, Schrodinger and Poisson equations are solved self consistently using\nquantum genetic algorithm (QGA). Thus, we have found the potential profile, the\nground state subband energy and their corresponding envelope functions, Fermi\nlevel, and the amount of tunneling charge from barrier to channel region. Their\ndependence on various device parameters are also examined.", "category": "cond-mat_other" }, { "text": "Residual attractive force between superparamagnetic nanoparticles: A superparamagnetic nanoparticle (SPN) is a nanometre-sized piece of a\nmaterial that would, in bulk, be a permanent magnet. In the SPN the individual\natomic spins are aligned via Pauli effects into a single giant moment that has\neasy orientations set by shape or magnetocrystalline anisotropy. Above a\nsize-dependent blocking temperature $T_{b}(V,\\tau_{obs})$, thermal fluctuations\ndestroy the average moment by flipping the giant spin between easy orientations\nat a rate that is rapid on the scale of the observation time $\\tau_{obs}$.\n We show that, depite the vanising of the average moment, two SPNs experience\na net attractive force of magnetic origin, analogous to the van der Waals force\nbetween molecules that lack a permanent electric dipole. This could be relevant\nfor ferrofluids, for the clumping of SPNs used for drug delivery, and for\nultra-dense magnetic recording media.", "category": "cond-mat_other" }, { "text": "Spin wave diffraction model for perpendicularly magnetized films: We present a near-field diffraction model for spin waves in perpendicularly\nmagnetized films applicable in any geometries of excitation fields. This model\nrelies on Kalinikos-Slavin formalism to express the dynamic susceptibility\ntensor in k-space, and calculate the diffraction patterns via inverse\n2D-Fourier transform of the response functions. We show an excellent\nquantitative agreement between our model and MuMax3 micro-magnetic simulations\non two different geometries of antennas. Our method benchmarks spin wave\ndiffraction in perpendicularly magnetized films, and is readily applicable for\nfuture designs of magnon beamforming and interferometric devices.", "category": "cond-mat_other" }, { "text": "Extraordinary wetting phase diagram for mixtures of Bose-Einstein\n condensates: The possibility of wetting phase transitions in Bose-Einstein condensed gases\nis predicted on the basis of Gross-Pitaevskii theory. The surface of a binary\nmixture of Bose-Einstein condensates can undergo a first-order wetting phase\ntransition upon varying the interparticle interactions, using, e.g., Feshbach\nresonances. Interesting ultralow-temperature effects shape the wetting phase\ndiagram. The prewetting transition is, contrary to general expectations, not of\nfirst order but critical, and the prewetting line does not meet the bulk phase\ncoexistence line tangentially. Experimental verification of these extraordinary\nresults is called for, especially now that it has become possible, using\noptical methods, to realize a planar \"hard wall\" boundary for the condensates.", "category": "cond-mat_other" }, { "text": "Three-fermion problems in optical lattices: We present exact results for the spectra of three fermionic atoms in a single\nwell of an optical lattice. For the three lowest hyperfine states of Li6 atoms,\nwe find a Borromean state across the region of the distinct pairwise Feshbach\nresonances. For K40 atoms, nearby Feshbach resonances are known for two of the\npairs, and a bound three-body state develops towards the positive\nscattering-length side. In addition, we study the sensitivity of our results to\natomic details. The predicted few-body phenomena can be realized in optical\nlattices in the limit of low tunneling.", "category": "cond-mat_other" }, { "text": "Coherent spinor dynamics in a spin-1 Bose condensate: Collisions in a thermal gas are perceived as random or incoherent as a\nconsequence of the large numbers of initial and final quantum states accessible\nto the system. In a quantum gas, e.g. a Bose-Einstein condensate or a\ndegenerate Fermi gas, the phase space accessible to low energy collisions is so\nrestricted that collisions be-come coherent and reversible. Here, we report the\nobservation of coherent spin-changing collisions in a gas of spin-1 bosons.\nStarting with condensates occupying two spin states, a condensate in the third\nspin state is coherently and reversibly created by atomic collisions. The\nobserved dynamics are analogous to Josephson oscillations in weakly connected\nsuperconductors and represent a type of matter-wave four-wave mixing. The\nspin-dependent scattering length is determined from these oscillations to be\n-1.45(18) Bohr. Finally, we demonstrate coherent control of the evolution of\nthe system by applying differential phase shifts to the spin states using\nmagnetic fields.", "category": "cond-mat_other" }, { "text": "Dynamical equations for time-ordered Green's functions: from the Keldysh\n time-loop contour to equilibrium at finite and zero temperature: We study the dynamical equation of the time-ordered Green's function at\nfinite temperature. We show that the time-ordered Green's function obeys a\nconventional Dyson equation only at equilibrium and in the limit of\nzero-temperature. In all other cases, i.e. finite-temperature at equilibrium or\nnon-equilibrium, the time-ordered Green's function obeys instead a modified\nDyson equation. The derivation of this result is obtained from the general\nformalism of the non-equilibrium Green's functions on the Keldysh time-loop\ncontour. At equilibrium, our result is fully consistent with the Matsubara\ntemperature Green's function formalism and also justifies rigorously the\ncorrection terms introduced in an ad hoc way with Hedin and Lundqvist. Our\nresults show that one should use the appropriate dynamical equation for the\ntime-ordered Green's function when working beyond the equilibrium\nzero-temperature limit.", "category": "cond-mat_other" }, { "text": "Suppression of Superfluidity of $^4$He in a Nanoporous Glass by\n Preplating a Kr Layer: Helium in nanoporous media has attracted much interest as a model Bose system\nwith disorder and confinement. Here we have examined how a change in porous\nstructure by preplating a monolayer of krypton affects the superfluid\nproperties of $^4$He adsorbed or confined in a nanoporous Gelsil glass, which\nhas a three-dimensional interconnected network of nanopores of 5.8 nm in\ndiameter. Isotherms of adsorption and desorption of nitrogen show that\nmonolayer preplating of Kr decreases the effective pore diameter to 4.7 nm and\nbroadens the pore size distribution by about eight times from the sharp\ndistribution of the bare Gelsil sample. The superfluid properties were studied\nby a torsional oscillator for adsorbed film states and pressurized liquid\nstates, both before and after the monolayer Kr preplating. In the film states,\nboth the superfluid transition temperature $T_{\\mathrm c}$ and the superfluid\ndensity decrease about 10 percent by Kr preplating. The suppression of film\nsuperfluidity is attributed to the quantum localization of $^4$He atoms by the\nrandomness in the substrate potential, which is caused by the\npreplating--induced broadening of the pore size distribution. In the\npressurized liquid states, the superfluid density $\\rho_{\\mathrm s}$ is found\nto increase by 10 percent by Kr preplating, whereas $T_{\\mathrm c}$ is\ndecreased by 2 percent at all pressures. The unexpected enhancement of\n$\\rho_{\\mathrm s}$ might indicate the existence of an unknown disorder effect\nfor confined $^4$He.", "category": "cond-mat_other" }, { "text": "Bounds for the Superfluid Fraction from Exact Quantum Monte Carlo Local\n Densities: For solid 4He and solid p-H2, using the flow-energy-minimizing one-body phase\nfunction and exact T=0 K Monte Carlo calculations of the local density, we have\ncalculated the phase function, the velocity profile and upper bounds for the\nsuperfluid fraction f_s. At the melting pressure for solid 4He we find that f_s\n< 0.20-0.21, about ten times what is observed. This strongly indicates that the\ntheory for the calculation of these upper bounds needs substantial\nimprovements.", "category": "cond-mat_other" }, { "text": "Ultracold Atoms in 1D Optical Lattices: Mean Field, Quantum Field,\n Computation, and Soliton Formation: In this work, we highlight the correspondence between two descriptions of a\nsystem of ultracold bosons in a one-dimensional optical lattice potential: (1)\nthe discrete nonlinear Schr\\\"{o}dinger equation, a discrete mean-field theory,\nand (2) the Bose-Hubbard Hamiltonian, a discrete quantum-field theory. The\nformer is recovered from the latter in the limit of a product of local coherent\nstates. Using a truncated form of these mean-field states as initial\nconditions, we build quantum analogs to the dark soliton solutions of the\ndiscrete nonlinear Schr\\\"{o}dinger equation and investigate their dynamical\nproperties in the Bose-Hubbard Hamiltonian. We also discuss specifics of the\nnumerical methods employed for both our mean-field and quantum calculations,\nwhere in the latter case we use the time-evolving block decimation algorithm\ndue to Vidal.", "category": "cond-mat_other" }, { "text": "Negative refraction and plano-concave lens focusing in one-dimensional\n photonic crystals: Negative refraction is demonstrated in one-dimensional (1D) dielectric\nphotonic crystals (PCs) at microwave frequencies. Focusing by plano-concave\nlens made of 1D PC due to negative refraction is also demonstrated. The\nfrequency-dependent negative refractive indices, calculated from the\nexperimental data matches very well with those determined from band structure\ncalculations. The easy fabrication of one-dimensional photonic crystals may\nopen the door for new applications.", "category": "cond-mat_other" }, { "text": "Exchange coupling in transition metal monoxides: Electronic structure\n calculations: An ab initio study of magnetic exchange interactions in antiferromagnetic and\nstrongly correlated 3d transition metal monoxides is presented. Their\nelectronic structure is calculated using the local self-interaction correction\napproach, implemented within the Korringa-Kohn-Rostoker band structure method,\nwhich is based on multiple scattering theory. The Heisenberg exchange constants\nare evaluated with the magnetic force theorem. Based on these the corresponding\nNeel temperatures T_N and spin wave dispersions are calculated. The Neel\ntemperatures are obtained using mean field approximation, random phase\napproximation and Monte Carlo simulations. The pressure dependence of T_N is\ninvestigated using exchange constants calculated for different lattice\nconstants. All the calculated results are compared to experimental data.", "category": "cond-mat_other" }, { "text": "Low frequency excitations of C60 chains inserted inside single-walled\n carbon nanotubes: The low frequency excitations of C60 chains inserted inside single-walled\ncarbon nanotubes (SWNTs) have been studied by inelastic neutron scattering\n(INS) on a high quality sample of peapods. The comparison of the\nneutron-derived generalized phonon density of states (GDOS) of the peapods\nsample with that of a raw SWNTs allows the vibrational properties of the C60\nchains encapsulated in the hollow core of the SWNTs to be probed. Lattice\ndynamical models are used to calculate the GDOS of chains of monomers, dimers\nand polymers inserted into SWNTs, which are compared to the experimental data.\nThe presence of strong interactions between C60 cages inside the nanotube is\nclearly demonstrated by an excess of mode density in the frequency range around\n10 meV. However, the presence of a quasi-elastic signal indicates that some of\nthe C60\\'s undergo rotational motion. This suggests that peapods are made from\na mixture of C60 monomers and C60 n-mer (dimer, trimer ... polymer) structures.", "category": "cond-mat_other" }, { "text": "A Derivation of the Classical Einstein-Dirac-Maxwell Equations From a\n Model of an Elastic Medium: Starting from a model of an elastic medium, partial differential equations\nwith the form of the coupled Einstein-Dirac-Maxwell equations are derived. The\nform of these equations describes particles with mass and spin coupled to\nelectromagnetic and gravitational type of interactions. A two dimensional\nversion of these equations is obtained by starting with a model in three\ndimensions and deriving equations for the dynamics of the lowest fourier modes\nassuming one dimension to be periodic. Generalizations to higher dimensions are\ndiscussed.", "category": "cond-mat_other" }, { "text": "Plasmonic engineering of metal nanoparticles for enhanced fluorescence\n and Raman scattering: We have investigated the effects of tuning the localized surface plasmon\nresonances (LSPRs) of silver nanoparticles on the fluorescence intensity,\nlifetime, and Raman signal from nearby fluorophores. The presence of a metallic\nstructure can alter the optical properties of a molecule by increasing the\nexcitation field, and by modifying radiative and non-radiative decay\nmechanisms. By careful choice of experimental parameters we have been able to\ndecouple these effects. We observe a four-fold increase in fluorescence\nenhancement and an almost 30-fold increase in decay rate from arrays of Ag\nnanoparticles, when the LSPR is tuned to the emission wavelength of a locally\nsituated fluorophore. This is consistent with a greatly increased efficiency\nfor energy transfer from fluorescence to surface plasmons. Additionally,\nsurface enhanced Raman scattering (SERS) measurements show a maximum\nenhancement occurs when both the incident laser light and the Raman signal are\nnear resonance with the plasmon energy. Spatial mapping of the SERS signal from\na nanoparticle array reveals highly localized differences in the excitation\nfield resulting from small differences in the LSPR energy.", "category": "cond-mat_other" }, { "text": "Effective magnetic fields in degenerate atomic gases induced by light\n beams with orbital angular momenta: We investigate the influence of two resonant laser beams on the mechanical\nproperties of degenerate atomic gases. The control and probe beams of light are\nconsidered to have Orbital Angular Momenta (OAM) and act on the three-level\natoms in the Electromagnetically Induced Transparency (EIT) configuration. The\ntheory is based on the explicit analysis of the quantum dynamics of cold atoms\ncoupled with two laser beams. Using the adiabatic approximation, we obtain an\neffective equation of motion for the atoms driven to the dark state. The\nequation contains a vector potential type interaction as well as an effective\ntrapping potential. The effective magnetic field is shown to be oriented along\nthe propagation direction of the control and probe beams containing OAM. Its\nspatial profile can be controlled by choosing proper laser beams. We\ndemonstrate how to generate a constant effective magnetic field, as well as a\nfield exhibiting a radial distance dependence. The resulting effective magnetic\nfield can be concentrated within a region where the effective trapping\npotential holds the atoms. The estimated magnetic length can be considerably\nsmaller than the size of the atomic cloud.", "category": "cond-mat_other" }, { "text": "Comments on \"Mixed Bose-Fermi statistics Kinetic equation and navigation\n through network\" by S.F. Chekmarev, Phys. Rev. E 82, 026106 (2010): The paper shows that the kinetic equations considered in [1], equilibrium\ndistribution obtained in [1], and results and conclusions obtained on the basis\nof the kinetic equation derived in [1] do not correspond to the mixed\nBose-Fermi statistics. Moreover, it is shown that the kinetic equation\ncorresponding to the case when the copies of the system are characterized by\ndifferent values of the fraction of the Fermi-like moves is incorrect. We\npresent a correct kinetic equation for the mixture of the Bose and Fermi moves\nand obtained the equilibrium distribution for the case when the probability of\nthe Fermi moves is higher or equal to that of the Bose moves.", "category": "cond-mat_other" }, { "text": "Exact Solitonic Solutions of the Gross-Pitaevskii Equation with a Linear\n Potential: We derive classes of exact solitonic solutions of the time-dependent\nGross-Pitaevskii equation with repulsive and attractive interatomic\ninteractions. The solutions correspond to a string of bright solitons with\nphase difference between adjacent solitons equal to $\\pi$. While the relative\nphase, width, and distance between adjacent solitons turn out to be a constant\nof the motion, the center of mass of the string moves with a constant\nacceleration arising from the inhomogeneity of the background.", "category": "cond-mat_other" }, { "text": "Bright-Dark Soliton Complexes in Spinor Bose-Einstein Condensates: We present bright-dark vector solitons in quasi-one-dimensional spinor (F=1)\nBose-Einstein condensates. Using a multiscale expansion technique, we reduce\nthe corresponding nonintegrable system of three coupled Gross-Pitaevskii\nequations (GPEs) to a completely integrable Yajima-Oikawa system. In this way,\nwe obtain approximate solutions for small-amplitude vector solitons of\ndark-dark-bright and bright-bright-dark types, in terms of the $m_{F}=+1,-1,0$\nspinor components, respectively. By means of numerical simulations of the full\nGPE system, we demonstrate that these states indeed feature soliton properties,\ni.e., they propagate undistorted and undergo quasi-elastic collisions. It is\nalso shown that, in the presence of a parabolic trap of strength $\\omega $, the\nbright component(s) is (are) guided by the dark one(s), and, as a result, the\nsmall-amplitude vector soliton as a whole performs harmonic oscillations of\nfrequency $\\omega/ \\sqrt{2}$ in the shallow soliton limit. We investigate\nnumerically deviations from this prediction, as the depth of the solitons is\nincreased, as well as when the strength of the spin-dependent interaction is\nmodified.", "category": "cond-mat_other" }, { "text": "Casimir-like force arising from quantum fluctuations in a slow-moving\n dilute Bose-Einstein condensate: We calculate a force due to zero-temperature quantum fluctuations on a\nstationary object in a moving superfluid flow. We model the object by a\nlocalized potential varying only in the flow direction and model the flow by a\nthree-dimensional weakly interacting Bose-Einstein condensate at zero\ntemperature. We show that this force exists for any arbitrarily small flow\nvelocity and discuss the implications for the stability of superfluid flow.", "category": "cond-mat_other" }, { "text": "Equation of state of an interacting Bose gas at finite temperature: a\n Path Integral Monte Carlo study: By using exact Path Integral Monte Carlo methods we calculate the equation of\nstate of an interacting Bose gas as a function of temperature both below and\nabove the superfluid transition. The universal character of the equation of\nstate for dilute systems and low temperatures is investigated by modeling the\ninteratomic interactions using different repulsive potentials corresponding to\nthe same s-wave scattering length. The results obtained for the energy and the\npressure are compared to the virial expansion for temperatures larger than the\ncritical temperature. At very low temperatures we find agreement with the\nground-state energy calculated using the diffusion Monte Carlo method.", "category": "cond-mat_other" }, { "text": "Self-localized impurities embedded in a one dimensional Bose-Einstein\n condensate and their quantum fluctuations: We consider the self-localization of neutral impurity atoms in a\nBose-Einstein condensate in a 1D model. Within the strong coupling approach, we\nshow that the self-localized state exhibits parametric soliton behavior. The\ncorresponding stationary states are analogous to the solitons of non-linear\noptics and to the solitonic solutions of the Schroedinger-Newton equation\n(which appears in models that consider the connection between quantum mechanics\nand gravitation). In addition, we present a Bogoliubov-de-Gennes formalism to\ndescribe the quantum fluctuations around the product state of the strong\ncoupling description. Our fluctuation calculations yield the excitation\nspectrum and reveal considerable corrections to the strong coupling\ndescription. The knowledge of the spectrum allows a spectroscopic detection of\nthe impurity self-localization phenomenon.", "category": "cond-mat_other" }, { "text": "Fundamental limits to nonlinear energy harvesting: Ease of miniaturization, and less or no maintenance, among other advantages,\nhave pushed towards replacement of conventional batteries with energy\nharvesters in particular, vibratory energy harvesters. In the recent years,\nnonlinearity has been intentionally introduced into the otherwise linear energy\nharvesters in the hope of increasing the frequency bandwidth and power density.\nHowever, fundamental limits on the harvestable energy of a harvester subjected\nto an arbitrary excitation force is yet unknown. Understanding of these limits\nis not only essential for assessment of the technology potential, but also\nprovides a broader prospective on the current harvesting mechanisms and\nguidance in their improvement. Here we derive the fundamental limits on output\npower of an ideal energy harvester, and develop an analysis framework for\nsimple computation of this limit for more sophisticated set-ups. We show that\nthe optimal harvester maximizes the harvested energy through a mechanical\nanalogue of 'buy low-sell high' strategy. Inspired by this strategy we propose\na novel concept of latch-assisted harvesting that is shown to harvest energy\nmore efficiently than its linear and bistable counterparts over a wider range\nof excitation frequencies and amplitudes.", "category": "cond-mat_other" }, { "text": "Dynamics of kicked matter-wave solitons in an optical lattice: We investigate effects of the application of a kick to one-dimensional\nmatter-wave solitons in a self-attractive Bose-Einstein condensate trapped in a\noptical lattice. The resulting soliton's dynamics is studied within the\nframework of the time-dependent nonpolynomial Schrodinger equation. The\ncrossover from the pinning to quasi-free motion crucially depends on the size\nof the kick, strength of the self-attraction, and parameters of the optical\nlattice.", "category": "cond-mat_other" }, { "text": "Construction of localized atomic wave packets: It is shown that highly localized solitons can be created in lower\ndimensional Bose-Einstein condensates (BEC), trapped in a regular harmonic\ntrap, by temporally varying the trap frequency. A BEC trapped in such a trap\ncan be effectively used to construct a pulsed atomic laser emitting coherent\natomic wave packets. It is also shown that one has complete control over the\nspatio-temporal dynamics of the solitons. The dynamics of these solitons are\ncompared with those constructed in a BEC where the trap frequency is constant.", "category": "cond-mat_other" }, { "text": "Evidence of Luttinger liquid behavior in one-dimensional dipolar quantum\n gases: The ground state and structure of a one-dimensional Bose gas with dipolar\nrepulsions is investigated at zero temperature by a combined Reptation Quantum\nMonte Carlo (RQMC) and bosonization approach. A non trivial Luttinger-liquid\nbehavior emerges in a wide range of intermediate densities, evolving into a\nTonks-Girardeau gas at low density and into a classical quasi-ordered state at\nhigh density. The density dependence of the Luttinger exponent is extracted\nfrom the numerical data, providing analytical predictions for observable\nquantities, such as the structure factor and the momentum distribution. We\ndiscuss the accessibility of such predictions in current experiments with\nultracold atomic and molecular gases.", "category": "cond-mat_other" }, { "text": "Symmetry-Protected Topological relationship between $SU(3)$ and\n $SU(2)\\times{U(1)}$ in Two Dimension: Symmetry-protected topological $\\left(SPT\\right)$ phases are gapped\nshort-range entangled states with symmetry $G$, which can be systematically\ndescribed by group cohomology theory. $SU(3)$ and $SU(2)\\times{U(1)}$ are\nconsidered as the basic groups of Quantum Chromodynamics and\nWeak-Electromagnetic unification, respectively. In two dimension $(2D)$,\nnonlinear-sigma models with a quantized topological Theta term can be used to\ndescribe nontrivial SPT phases. By coupling the system to a probe field and\nintegrating out the group variables, the Theta term becomes the effective\naction of Chern-Simons theory which can derive the response current density. As\na result, the current shows a spin Hall effect, and the quantized number of the\nspin Hall conductance of SPT phases $SU(3)$ and $SU(2)\\times{U(1)}$ are same.\nIn addition, relationships between $SU(3)$ and $SU(2)\\times{U(1)}$ which maps\n$SU(3)$ to $SU(2)$ with a rotation $U(1)$ will be given.", "category": "cond-mat_other" }, { "text": "X-ray Studies of Structure and Defects in Solid 4He from 50 mK to\n Melting: Recent measurements have found non-classical rotational inertia (NCRI) in\nsolid 4He starting at T ~ 200 mK, leading to speculation that a supersolid\nstate may exist in these materials. Differences in the NCRI fraction due to the\ngrowth method and annealing history imply that defects play an important role\nin the effect. Using x-ray synchrotron radiation, we have studied the nature of\nthe crystals and the properties of the defects in solid 4He at temperatures\ndown to 50 mK. Measurements of peak intensities and lattice parameters do not\nshow indications of the supersolid transition. Using growth methods similar to\nthose of groups measuring the NCRI we find that large crystals form. Scanning\nwith a small (down to 10 x 10 um2) beam, we resolve a mosaic structure within\nthese crystals consistent with numerous small angle grain boundaries. The\nmosaic shows significant shifts over time even at temperatures far from\nmelting. We discuss the relevance of these defects to the NCRI observations.", "category": "cond-mat_other" }, { "text": "Quantum fluctuation-induced uniaxial and biaxial spin nematics: It is shown that zero point quantum fluctuations (ZPQFs) completely lift the\naccidental continuous degeneracy that is found in mean field analysis of\nquantum spin nematic phases of hyperfine spin 2 cold atoms. The result is two\ndistinct ground states which have higher symmetries: a uniaxial spin nematic\nand a biaxial spin nematic with dihedral symmetry ${Dih}_4$. There is a novel\nfirst order quantum phase transition between the two phases as atomic\nscattering lengths are varied. We find that the ground state of $^{87}Rb$ atoms\nshould be a uniaxial spin nematic. We note that the energy barrier between the\nphases could be observable in dynamical experiments.", "category": "cond-mat_other" }, { "text": "Volume element structure and roton-maxon-phonon excitations in\n superfluid helium beyond the Gross-Pitaevskii approximation: We propose a theory which deals with the structure and interactions of volume\nelements in liquid helium II. The approach consists of two nested models linked\nvia parametric space. The short-wavelength part describes the interior\nstructure of the fluid element using a non-perturbative approach based on the\nlogarithmic wave equation; it suggests the Gaussian-like behaviour of the\nelement's interior density and interparticle interaction potential. The\nlong-wavelength part is the quantum many-body theory of such elements which\ndeals with their dynamics and interactions. Our approach leads to a unified\ndescription of the phonon, maxon and roton excitations, and has noteworthy\nagreement with experiment: with one essential parameter to fit we reproduce at\nhigh accuracy not only the roton minimum but also the neighboring local maximum\nas well as the sound velocity and structure factor.", "category": "cond-mat_other" }, { "text": "Rotating quantum turbulence in superfluid 4He in the T=0 limit: Observations of quantum turbulence in pure superfluid 4He in a rotating\ncontainer are reported. New techniques of large-scale forcing (rotational\noscillations of the cubic container) and detecting (monitoring ion transport\nalong the axis of rotation) turbulence were implemented. Near the axial walls,\nwith increasing forcing the vortex tangle grows without an observable\nthreshold. This tangle gradually develops into bulk turbulence at a\ncharacteristic amplitude of forcing that depends on forcing frequency and\nrotation rate. At higher amplitudes, the total vortex line length increases\nrapidly. Resonances of inertial waves are observed in both laminar and\nturbulent bulk states. On such resonances, the turbulence appears at smaller\namplitudes of forcing.", "category": "cond-mat_other" }, { "text": "The growth of a Super Stable Heap : an experimental and numerical study: We report experimental and numerical results on the growth of a super stable\nheap (SSH). Such a regime appears for flows in a thin channel and for high flow\nrate : the flow occurs atop a nearly static heap whose angle is stabilized by\nthe flowing layer at its top and the side wall friction. The growth of the\nstatic heap is investigated in this paper. A theoretical analysis inspired by\nthe BRCE formalism predicts the evolution of the growth process, which is\nconfirmed by both experiments and numerical simulations. The model allows us to\nlink the characteristic time of the growth to the exchange rate between the\n\"moving\" and \"static\" grains. We show that this rate is proportional to the\nheight of the flowing layer even for thick flows. The study of upstream\ntraveling waves sheds new light on the BCRE model.", "category": "cond-mat_other" }, { "text": "Correlation of the angular dependence of spin-transfer torque and giant\n magnetoresistance in the limit of diffusive transport in spin valves: Angular variation of giant magnetoresistance and spin-transfer torque in\nmetallic spin-valve heterostructures is analyzed theoretically in the limit of\ndiffusive transport. It is shown that the spin-transfer torque in asymmetric\nspin valves can vanish in non-collinear magnetic configurations, and such a\nnon-standard behavior of the torque is generally associated with a\nnon-monotonic angular dependence of the giant magnetoresistance, with a global\nminimum at a non-collinear magnetic configuration.", "category": "cond-mat_other" }, { "text": "Basis-Independent Spectral Methods for Non-linear Optical Response in\n Arbitrary Tight-binding Models: In this paper, we developed a basis-independent perturbative method for\ncalculating the non-linear optical response of arbitrary non-interacting\ntight-binding models. Our method is based on the non-equilibrium Keldysh\nformalism and allows an efficient numerical implementation within the framework\nof the Kernel Polynomial Method for systems which are not required to be\ntranslation-invariant. Some proof-of-concept results of the second-order\noptical conductivity are presented for the special case of gapped graphene with\nvacancies and an on-site Anderson disordered potential.", "category": "cond-mat_other" }, { "text": "Effective thermodynamics of strongly coupled qubits: Interactions between a quantum system and its environment at low temperatures\ncan lead to violations of thermal laws for the system. The source of these\nviolations is the entanglement between system and environment, which prevents\nthe system from entering into a thermal state. On the other hand, for two-state\nsystems, we show that one can define an effective temperature, placing the\nsystem into a `pseudo-thermal' state where effective thermal laws are upheld.\nWe then numerically explore these assertions for an n-state system inspired by\nthe spin-boson environment.", "category": "cond-mat_other" }, { "text": "Phase separations of bosonic mixtures in optical lattices from\n macroscopic to microscopic scales: Mixtures of cold bosonic atoms in optical lattices undergo phase separations\non different length scales with increasing inter-species repulsion. As a\ngeneral rule, the stronger the intra-species interactions, the shorter is this\nlength scale. The wealth of phenomena is documented by illustrative examples on\nboth superfluids and Mott-insulators.", "category": "cond-mat_other" }, { "text": "Artificial gravitation effect on spin-polarized exciton-polaritons: The pseudospin dynamics of long-living exciton-polaritons in a wedged 2D\ncavity has been studied theoretically accounting for the external magnetic\nfield effect. The cavity width variation plays the role of the artificial\ngravitational force acting on a massive particle: exciton-polariton. A\nsemi-classical model of the spin-polarization dynamics of ballistically\npropagating exciton-polaritons has been developed. It has been shown that for\nthe specific choise of the magnetic field magnitude and the initial polariton\nwave vector the polariton polarization vector tends to an attractor on the\nPoincare sphere. Based on this effect, the switching the polariton polarization\nin the ballistic regime has been demonstrated. The self-interference of the\npolariton field emitted by a point-like source has been shown to induce the\nformation of interference patterns reminiscent of the interference patterns of\ncylindrical and plane waves.", "category": "cond-mat_other" }, { "text": "Extremal transmission through a microwave photonic crystal and the\n observation of edge states in a rectangular Dirac billiard: This article presents experimental results on properties of waves propagating\nin an unbounded and a bounded photonic crystal consisting of metallic cylinders\nwhich are arranged in a triangular lattice. First, we present transmission\nmeasurements of plane waves traversing a photonic crystal. The experiments are\nperformed in the vicinity of a Dirac point, i.e., an isolated conical\nsingularity of the photonic band structure. There, the transmission shows a\npseudodiffusive 1/L dependence, with $L$ being the thickness of the crystal, a\nphenomenon also observed in graphene. Second, eigenmode intensity distributions\nmeasured in a microwave analog of a relativistic Dirac billiard, a rectangular\nmicrowave billiard that contains a photonic crystal, are discussed. Close to\nthe Dirac point states have been detected which are localized at the straight\nedge of the photonic crystal corresponding to a zigzag edge in graphene.", "category": "cond-mat_other" }, { "text": "Effective theory for the Goldstone field in the BCS-BEC crossover at T=0: We perform a detailed study of the effective Lagrangian for the Goldstone\nmode of a superfluid Fermi gas at zero temperature in the whole BCS-BEC\ncrossover. By using a derivative expansion of the response functions, we derive\nthe most general form of this Lagrangian at the next to leading order in the\nmomentum expansion in terms of four coefficient functions. This involves the\nelimination of all the higher order time derivatives by careful use of the\nleading order field equations. In the infinite scattering length limit where\nconformal invariance is realized, we show that the effective Lagrangian must\ncontain an unnoticed invariant combination of higher spatial gradients of the\nGoldstone mode, while explicit couplings to spatial gradients of the trapping\npotential are absent. Across the whole crossover, we determine all the\ncoefficient functions at the one-loop level, taking into account the dependence\nof the gap parameter on the chemical potential in the mean-field approximation.\nThese results are analytically expressed in terms of elliptic integrals of the\nfirst and second kind. We discuss the form of these coefficients in the extreme\nBCS and BEC regimes and around the unitary limit, and compare with recent work\nby other authors.", "category": "cond-mat_other" }, { "text": "Relaxation of Bose-Einstein Condensates of Magnons in Magneto-Textural\n Traps in Superfluid $^3$He-B: In superfluid $^3$He-B externally pumped quantized spin-wave excitations or\nmagnons spontaneously form a Bose-Einstein condensate in a 3-dimensional trap\ncreated with the order-parameter texture and a shallow minimum in the\npolarizing field. The condensation is manifested by coherent precession of the\nmagnetization with a common frequency in a large volume. The trap shape is\ncontrolled by the profile of the applied magnetic field and by the condensate\nitself via the spin-orbit interaction. The trapping potential can be\nexperimentally determined with the spectroscopy of the magnon levels in the\ntrap. We have measured the decay of the ground state condensates after\nswitching off the pumping in the temperature range $(0.14\\div\n0.2)T_{\\mathrm{c}}$. Two contributions to the relaxation are identified: (1)\nspin-diffusion with the diffusion coefficient proportional to the density of\nthermal quasiparticles and (2) the approximately temperature-independent\nradiation damping caused by the losses in the NMR pick-up circuit. The measured\ndependence of the relaxation on the shape of the trapping potential is in a\ngood agreement with our calculations based on the magnetic field profile and\nthe magnon-modified texture. Our values for the spin diffusion coefficient at\nlow temperatures agree with the theoretical prediction and earlier measurements\nat temperatures above $0.5T_{\\mathrm{c}}$.", "category": "cond-mat_other" }, { "text": "Stability of Formation of Large Bipolaron: Nonrelativistic Quantum Field\n Theory: We are concerned with the stability of formation of large bipolaron in a\n3-dimensional (3D) crystal. This problem is considered in the framework of\nnonrelativistic quantum field theory. Thus, the Hamiltonian formalism, as\nFroehlich introduced, is employed to describe the bipolaron. We approach the\nproblem by characterizing some sufficient or necessary conditions for the\nbipolaron being stable. This paper gives a full detail of the author's talks at\nESI, RIMS, and St. Petersburg State Univ. in 2005.", "category": "cond-mat_other" }, { "text": "Proposed definitions of the correlation energy density from a\n Hartree-Fock starting point: The two-electron Moshinsky model atom as an\n exactly solvable model: In both molecular physics and condensed matter theory, deeper understanding\nof the correlation energy density epsilon_c (r) remains a high priority. By\nadopting Loewdin's definition of correlation energy as the difference between\nthe exact and the Hartree-Fock values, here we propose two alternative routes\nto define this. One of these involves both exact and Hartree-Fock (HF)\nwavefunctions, while the second requires a coupling constant integration. As an\nexact analytical example of the first route, we treat the two-electron model\natom of Moshinsky, for which both confinement potential and interactions are\nharmonic. Though the correlation energy density epsilon_c (r) is known\nanalytically, we also investigate numerically its relation to the exact\nground-state density in this example.", "category": "cond-mat_other" }, { "text": "Vortices in Atomic Bose-Einstein Condensates in the Large Gas Parameter\n Region: In this work we compare the results of the Gross-Pitaevskii and modified\nGross-Pitaevskii equations with ab initio variational Monte Carlo calculations\nfor Bose-Einstein condensates of atoms in axially symmetric traps. We examine\nboth the ground state and excited states having a vortex line along the z-axis\nat high values of the gas parameter and demonstrate an excellent agreement\nbetween the modified Gross-Pitaevskii and ab initio Monte Carlo methods, both\nfor the ground and vortex states.", "category": "cond-mat_other" }, { "text": "Propagation of thermal excitations in a cluster of vortices in\n superfluid 3He-B: We describe the first measurement on Andreev scattering of thermal\nexcitations from a vortex configuration with known density, spatial extent, and\norientations in 3He-B superfluid. The heat flow from a blackbody radiator in\nequilibrium rotation at constant angular velocity is measured with two quartz\ntuning fork oscillators. One oscillator creates a controllable density of\nexcitations at 0.2Tc base temperature and the other records the thermal\nresponse. The results are compared to numerical calculations of ballistic\npropagation of thermal quasiparticles through a cluster of rectilinear\nvortices.", "category": "cond-mat_other" }, { "text": "Pekar's Ansatz and the Strong Coupling Problem in Polaron Theory: A detailed consideration is given to the translation-invariant theory of\nTulub polaron constructed without the use of Pekar ansatz. A fundamental result\nof the theory is that the value of the polaron energy is lower than that\nobtained on the basis of Pekar ansatz which was considered as an asymptotically\nexact solution in the strong coupling limit. In the case of bipolarons the\ntheory yields the best values of the coupling energy and critical parameters of\ntheir stability. Numerous physical consequences of the existence of\ntranslation-invariant polarons and bipolarons are discussed.", "category": "cond-mat_other" }, { "text": "Vortex quantum creation and winding number scaling in a quenched spinor\n Bose gas: Motivated by a recent experiment, we study non-equilibrium quantum phenomena\ntaking place in the quench of a spinor Bose-Einstein condensate through the\nzero-temperature phase transition separating the polar paramagnetic and planar\nferromagnetic phases. We derive the typical spin domain structure (correlations\nof the effective magnetization) created by the quench arising due to spin-mode\nquantum fluctuations, and establish a sample-size scaling law for the creation\nof spin vortices, which are topological defects in the transverse\nmagnetization.", "category": "cond-mat_other" }, { "text": "Fully permanent magnet atom chip for Bose-Einstein condensation: We describe a self-biased, fully permanent magnet atom chip used to study\nultracold atoms and to produce a Bose-Einstein condensate (BEC). The magnetic\ntrap is loaded efficiently by adiabatic transport of a magnetic trap via the\napplication of uniform external fields. Radio frequency spectroscopy is used\nfor in-trap analysis and to determine the temperature of the atomic cloud. The\nformation of a Bose-Einstein condensate is observed in time of flight images\nand as a narrow peak appearing in the radio frequency spectrum.", "category": "cond-mat_other" }, { "text": "Bosonic enhancement of spontaneous emission near an interface: We show how the spontaneous emission rate of an excited two-level atom placed\nin a trapped Bose-Einstein condensate of ground-state atoms is enhanced by\nbosonic stimulation. This stimulation depends on the overlap of the excited\nmatter-wave packet with the macroscopically occupied condensate wave function,\nand provides a probe of the spatial coherence of the Bose gas. The effect can\nbe used to amplify the distance-dependent decay rate of an excited atom near an\ninterface.", "category": "cond-mat_other" }, { "text": "Strong linewidth variation for spin-torque nano-oscillators as a\n function of in-plane magnetic field angle: We measure the microwave signals produced by spin-torque-driven magnetization\ndynamics in patterned magnetic multilayer devices at room temperature, as a\nfunction of the angle of a magnetic field applied in the sample plane. We find\nstrong variations in the frequency linewidth of the signals, with a decrease by\nmore than a factor of 20 as the field is rotated from the magnetic easy axis to\nthe in-plane hard axis. Based on micromagnetic simulations, we identify these\nvariations as due to a transition from spatially incoherent to coherent\nprecession.", "category": "cond-mat_other" }, { "text": "Calculation of Kapitza resistance with kinetic equation: A new method is introduced for calculation of interfacial thermal resistance\nin the case of heat transport through the interface by phonons. A unique\nfeature of the method is taking into account all the consequences of a\nnon-equilibrium character of phonon distribution functions during the heat\ntransport. We introduce a model set of transmission and reflection amplitudes\nof phonons at the interface based on the most common in the literature\nDiffusive Mismatch Model. For the proposed model we derive an exact analytical\nsolution. The problem is also solved for a set of transmission and reflection\namplitudes characterized by a free parameter. We found that the calculation\nresults are in a good agreement with the experimental data.", "category": "cond-mat_other" }, { "text": "Bound-to-bound and bound-to-continuum optical transitions in combined\n quantum dot - superlattice systems: By combining band gap engineering with the self-organized growth of quantum\ndots, we present a scheme of adjusting the mid-infrared absorption properties\nto desired energy transitions in quantum dot based photodetectors. Embedding\nthe self organized InAs quantum dots into an AlAs/GaAs superlattice enables us\nto tune the optical transition energy by changing the superlattice period as\nwell as by changing the growth conditions of the dots. Using a one band\nenvelope function framework we are able, in a fully three dimensional\ncalculation, to predict the photocurrent spectra of these devices as well as\ntheir polarization properties. The calculations further predict a strong impact\nof the dots on the superlattices minibands. The impact of vertical dot\nalignment or misalignment on the absorption properties of this dot/superlattice\nstructure is investigated. The observed photocurrent spectra of vertically\ncoupled quantum dot stacks show very good agreement with the calculations.In\nthese experiments, vertically coupled quantum dot stacks show the best\nperformance in the desired photodetector application.", "category": "cond-mat_other" }, { "text": "Chiral structures of lander molecules on Cu(100): Supramolecular assemblies of lander molecules (C$_{90}$H$_{98}$) on Cu(100)\nare investigated with low-temperature scanning tunneling microscopy. The\nenergetically most favourable conformation of the adsorbed molecule is found to\nexist in two mirror symmetric enantiomers or conformers. At low coverage, the\nmolecules align in enantiomerically pure chains along the chiral directions\n$[01\\bar{2}],[02\\bar{1}],[012]$ and $[021]$. The arrangement is proposed to be\nmainly governed by intermolecular van-der-Waals interaction. At higher\ncoverages, the molecular chains arrange into chiral domains, for which a\nstructural model is presented.", "category": "cond-mat_other" }, { "text": "Stone-Wales Transformation Paths in Fullerene C60: The mechanisms of formation of a metastable defect isomer of fullerene C60\ndue to the Stone-Wales transformation are theoretically studied. It is\ndemonstrated that the paths of the \"dynamic\" Stone-Wales transformation at a\nhigh sufficient for overcoming potential barriers) temperature can differ from\nthe two \"adiabatic\" transformation paths discussed in the literature. This\nbehavior is due to the presence of a great near-flat segment of the\npotential-energy surface in the neighborhood of metastable states. Besides, the\nsequence of rupture and formation of interatomic bonds is other than that in\nthe case of the adiabatictransformation.", "category": "cond-mat_other" }, { "text": "Soliton Analysis of the Electro-Optical Response of Blue Bronze: In recent measurements on the charge-density-wave (CDW) conductor blue bronze\n(K0.3MoO3), the electro-transmittance and electro-reflectance spectra were\nsearched for intragap states that could be associated with solitons created by\ninjection of electrons into the CDW at the current contacts [Eur. Phys. J. B\n16, 295 (2000); ibid 35, 233 (2003)]. In this work, we adapt the model of\nsoliton absorption in dimerized polyacetylene to the blue bronze results, to\nobtain the (order of magnitude) estimate that current induced solitons occur on\nless than ~ 10% of the conducting chains. We discuss the implications of these\nresults on models of soliton lifetimes and motion of CDW phase dislocations.", "category": "cond-mat_other" }, { "text": "First-principles investigation of spin polarized conductance in atomic\n carbon wire: We analyze spin-dependent energetics and conductance for one dimensional (1D)\natomic carbon wires consisting of terminal magnetic (Co) and interior\nnonmagnetic (C) atoms sandwiched between gold electrodes, obtained employing\nfirst-principles gradient corrected density functional theory and Landauer's\nformalism for conductance. Wires containing an even number of interior carbon\natoms are found to be acetylenic with sigma-pi bonding patterns, while cumulene\nstructures are seen in wires containing odd number of interior carbon atoms, as\na result of strong pi-conjugation. Ground states of carbon wires containing up\nto 13 C atoms are found to have anti-parallel spin configurations of the two\nterminal Co atoms, while the 14 C wire has a parallel Co spin configuration in\nthe ground state. The stability of the anti-ferromagnetic state in the wires is\nascribed to a super-exchange effect. For the cumulenic wires this effect is\nconstant for all wire lengths. For the acetylenic wires, the super-exchange\neffect diminishes as the wire length increases, going to zero for the atomic\nwire containing 14 carbon atoms. Conductance calculations at the zero bias\nlimit show spin-valve behavior, with the parallel Co spin configuration state\ngiving higher conductance than the corresponding anti-parallel state, and a\nnon-monotonic variation of conductance with the length of the wires for both\nspin configurations.", "category": "cond-mat_other" }, { "text": "Tightly bound gap solitons in a Fermi gas: Within the framework of the mean-field-hydrodynamic model of a degenerate\nFermi gas (DFG), we study, by means of numerical methods and variational\napproximation (VA), the formation of fundamental gap solitons (FGSs) in a DFG\n(or in a BCS superfluid generated by weak interaction between spin-up and\nspin-down fermions), which is trapped in a periodic optical-lattice (OL)\npotential. An effectively one-dimensional (1D) configuration is considered,\nassuming strong transverse confinement; in parallel, a proper 1D model of the\nDFG (which amounts to the known quintic equation for the Tonks-Girardeau gas in\nthe OL) is considered too. The FGSs found in the first two bandgaps of the\nOL-induced spectrum (unless they are very close to edges of the gaps) feature a\ntightly-bound shape, being essentially confined to a single cell of the OL. In\nthe second bandgap, we also find antisymmetric tightly-bound subfundamental\nsolitons (SFSs), with zero at the midpoint. The SFSs are also confined to a\nsingle cell of the OL, but, unlike the FGSs, they are unstable. The predicted\nsolitons, consisting of $\\sim 10^4 - 10^5$ atoms, can be created by available\nexperimental techniques in the DFG of $^6$Li atoms.", "category": "cond-mat_other" }, { "text": "Quantum viscosity and the Reynolds similitude in quantum liquid He-II: Reynolds similitude, a key concept in hydrodynamics, states that two\nphenomena of different length scales with a similar geometry are physically\nidentical. Flow properties are universally determined in a unified way in terms\nof the Reynolds number ${\\cal R}$ (dimensionless, ratio of inertial to viscous\nforces in incompressible fluids). For example, the drag coefficient $c_D$ of\nobjects with similar shapes moving in fluids is expressed by a universal\nfunction of ${\\cal R}$. Certain studies introduced similar dimensionless\nnumbers, that is, the superfluid Reynolds number ${\\cal R}_s$, to characterize\nturbulent flows in superfluids. However, the applicablity of the similitude to\ninviscid quantum fluids is nontrivial as the original theory is applicable to\nviscous fluids. This study proposed a method to verify the similitude using\ncurrent experimental techniques in quantum liquid He-II. A highly precise\nrelation between $c_D$ and ${\\cal R}_s$ was obtained in terms of the terminal\nspeed of a macroscopic body falling in He-II at finite temperatures across the\nKnudsen (ballistic) and hydrodynamic regimes of thermal excitations. Reynolds\nsimilitude in superfluids can facilitate unified mutual development of\nclassical and quantum hydrodynamics.", "category": "cond-mat_other" }, { "text": "Resonant Atom-Dimer Relaxation in Ultracold Atoms: Three-body systems with large scattering length display universal phenomena\nassociated with a discrete scaling symmetry. These phenomena include resonant\nenhancement of three-body loss rates when an Efimov three-body resonance is at\nthe scattering threshold. In particular, there can be resonant peaks in the\natom-dimer relaxation rate for large positive scattering length. We improve\nupon earlier studies and calculate the atom-dimer relaxation rate as a function\nof temperature using a Bose-Einstein distribution for the thermal average. As\ninput, we use calculations of the atom-dimer scattering phase shifts from\neffective field theory.", "category": "cond-mat_other" }, { "text": "Magneto-optic far-infrared study of Sr$_{14}$Cu$_{24}$O$_{41}$: triplet\n excitations in chains: Using far-infrared spectroscopy we have studied the magnetic field and\ntemperature dependence of the spin gap modes in the chains of\nSr$_{14}$Cu$_{24}$O$_{41}$. Two triplet modes T$_1$ and T$_2$ were found in the\ncenter of the Brillouin zone at $\\Delta_1=9.65$ meV and $\\Delta_2=10.86$ meV in\nzero magnetic field. The T$_1$ mode was excited when the electric field vector\n${\\bf E}$ of the light was polarized along the b axis (perpendicular to the\nplanes of chains and ladders) and T$_2$ was excited for ${\\bf E}\\parallel {\\bf\na}$ (perpendicular to the chains and along the rungs). Up to the maximum\nmagnetic field of 18 T, applied along the chains, the electron $g$ factors of\nthese two modes were similar, $g_{1c}=2.049$ and $g_{2c}=2.044$. Full linewidth\nat half maximum for both modes was 1 cm$^{-1}$ (0.12 meV) at 4K and increased\nwith $T$. The temperature dependence of mode energies and line intensities was\nin agreement with the inelastic neutron scattering results from two groups\n[Matsuda {\\it et al.}, Phys. Rev. B {\\bf 59}, 1060 (1999) and Regnault {\\it et\nal.}, Phys. Rev. B {\\bf 59}, 1055 (1999)]. The T$_1$ mode has not been observed\nby inelastic neutron scattering in the points of the $k$-space equivalent to\nthe center of the Brillouin zone. Our study indicates that the zone structure\nmodel of magnetic excitations of Sr$_{14}$Cu$_{24}$O$_{41}$ must be modified to\ninclude a triplet mode at 9.65 meV in the center of the magnetic Brillouin\nzone.", "category": "cond-mat_other" }, { "text": "Diffusive Decay of the Vortex Tangle and Kolmogorov turbulence in\n quantum fluids: The idea that chaotic set of quantum vortices can mimic classical turbulence,\nor at least reproduce many main features, is currently actively being\ndeveloped. Appreciating significance of the challenging problem of the\nclassical turbulence it can be expressed that the idea to study it in terms of\nquantized line is indeed very important and may be regarded as a breakthrough.\nFor this reason, this theory should be carefully scrutinized. One of the basic\narguments supporting this point of view is the fact that vortex tangle decays\nat zero temperature, when the apparent mechanism of dissipation (mutual\nfriction) is absent. Since the all possible mechanisms of dissipation of the\nvortex energy, discussed in the literature, are related to the small scales, it\nis natural to suggest that the Kolmogorov cascade takes the place with the flow\nof the energy, just as in the classical turbulence. In a series of recent\nexperiment attenuation of vortex line density was observed and authors\nattribute this decay to the properties of the Kolmogorov turbulence. In the\npresent work we discuss alternative possibility of decay of the vortex tangle,\nwhich is not related to dissipation at small scales. This mechanism is just the\ndiffusive like spreading of the vortex tangle. We discuss a number of the key\nexperiments, considering them both from the point of view of alternative\nexplanation and of the theory of Kolmogorov turbulence in quantum fluids.", "category": "cond-mat_other" }, { "text": "Measurement and analysis of the Doppler broadened energy spectra of\n annihilation gamma radiation originating from clean and adsorbate-covered\n surfaces: We present measurements and theoretical modeling demonstrating the capability\nof Doppler Broadened annihilation gamma Spectroscopy (DBS) to provide\nelement-specific information from the topmost atomic layer of surfaces that are\neither clean or covered with adsorbates or thin films. Our measurements show\nthat the energy spectra of Doppler-shifted annihilation gamma photons emitted\nfollowing the annihilation of positrons from the topmost atomic layers of clean\ngold (Au) and copper (Cu) differ significantly. With the aid of the positron\nannihilation-induced Auger electron spectroscopy (PAES) performed\nsimultaneously with DBS, we show that measurable differences between the\nDoppler broadened gamma spectra from Au and Cu surfaces in the high energy\nregion of the gamma spectra can be used for the quantification of surface\nchemical composition. Modeling the measured Doppler spectra from clean Au and\nCu surfaces using gamma spectra obtained from ab initio calculations after\nconsidering the detector energy resolution and surface positronium formation\npointed to an increase in the relative contribution of gamma from positron\nannihilation with valence shell electrons. The fit result also suggests that\nthe surface-trapped positrons predominantly annihilated with the delocalized\nvalence shell (s and p) electrons that extended into the vacuum as compared to\nthe highly localized d electrons. Simultaneous DBS and PAES measurements from\nadsorbate (sulfur, oxygen, carbon) or thin film (selenium (Se), graphene)\ncovered Cu surface showed that it is possible to distinguish and quantify the\nsurface adsorbate and thin-film composition just based on DBS. DBS of elemental\nsurfaces presents a promising avenue for developing a characterization tool\nthat can be used to probe external and internal surfaces that are inaccessible\nby conventional surface science techniques.", "category": "cond-mat_other" }, { "text": "Three-body Recombination of Lithium-6 Atoms with Large Negative\n Scattering Lengths: The 3-body recombination rate at threshold for distinguishable atoms with\nlarge negative pair scattering lengths is calculated in the zero-range\napproximation. The only parameters in this limit are the 3 scattering lengths\nand the Efimov parameter, which can be complex valued. We provide semi-analytic\nexpressions for the cases of 2 or 3 equal scattering lengths and we obtain\nnumerical results for the general case of 3 different scattering lengths. Our\ngeneral result is applied to the three lowest hyperfine states of Lithium-6\natoms. Comparisons with recent experiments provide indications of loss features\nassociated with Efimov trimers near the 3-atom threshold.", "category": "cond-mat_other" }, { "text": "Repeating head-on collisions in an optical trap and the evaluation of\n spin-dependent interactions among neutral particles: A dynamic process of repeating collisions of a pair of trapped neutral\nparticles with weak spin-dependent interaction is designed and studied. Related\ntheoretical derivation and numerical calculation have been performed to study\nthe inherent coordinate-spin and momentum-spin correlation. Due to the\nrepeating collisions the effect of the weak interaction can be accumulated and\nenlarged, and therefore can be eventually detected. Numerical results suggest\nthat the Cr-Cr interaction, which has not yet been completely clear, could be\nthereby determined. The design can be in general used to determine various\ninteractions among neutral atoms and molecules, in particular for the\ndetermination of very weak forces.", "category": "cond-mat_other" }, { "text": "Spin excitations in a monolayer scanned by a magnetic tip: Energy dissipation via spin excitations is investigated for a hard\nferromagnetic tip scanning a soft magnetic monolayer. We use the classical\nHeisenberg model with Landau-Lifshitz-Gilbert (LLG)-dynamics including a\nstochastic field representing finite temperatures. The friction force depends\nlinearly on the velocity (provided it is small enough) for all temperatures.\nFor low temperatures, the corresponding friction coefficient is proportional to\nthe phenomenological damping constant of the LLG equation. This dependence is\nlost at high temperatures, where the friction coefficient decreases\nexponentially. These findings can be explained by properties of the spin\npolarization cloud dragged along with the tip.", "category": "cond-mat_other" }, { "text": "Generation of mesoscopic superpositions of a binary Bose-Einstein\n condensate in a slightly asymmetric double well: A previous publication [Europhysics Letters 78, 10009 (2007)] suggested to\ncoherently generate mesoscopic superpositions of a two-component Bose-Einstein\ncondensate in a double well under perfectly symmetric conditions. However,\nalready tiny asymmetries can destroy the entanglement properties of the ground\nstate. Nevertheless, even under more realistic conditions, the scheme is\ndemonstrated numerically to generate mesoscopic superpositions.", "category": "cond-mat_other" }, { "text": "Influence of interface structure on electronic properties and Schottky\n barriers in Fe/GaAs magnetic junctions: The electronic and magnetic properties of Fe/GaAs(001) magnetic junctions are\ninvestigated using first-principles density-functional calculations. Abrupt and\nintermixed interfaces are considered, and the dependence of charge transfer,\nmagnetization profiles, Schottky barrier heights, and spin polarization of\ndensities of states on interface structure is studied. With As-termination, an\nabrupt interface with Fe is favored, while Ga-terminated GaAs favors the\nformation of an intermixed layer with Fe. The Schottky barrier heights are\nparticularly sensitive to the abruptness of the interface. A significant\ndensity of states in the semiconducting gap arises from metal interface states.\nThese spin-dependent interface states lead to a significant minority spin\npolarization of the density of states at the Fermi level that persists well\ninto the semiconductor, providing a channel for the tunneling of minority spins\nthrough the Schottky barrier. These interface-induced gap states and their\ndependence on atomic structure at the interface are discussed in connection\nwith potential spin-injection applications.", "category": "cond-mat_other" }, { "text": "Parity-time symmetry breaking in magnetic systems: The understanding of out-of-equilibrium physics, especially dynamic\ninstabilities and dynamic phase transitions, is one of the major challenges of\ncontemporary science, spanning the broadest wealth of research areas that range\nfrom quantum optics to living organisms. Focusing on nonequilibrium dynamics of\nan open dissipative spin system, we introduce a non-Hermitian Hamiltonian\napproach, in which non-Hermiticity reflects dissipation and deviation from\nequilibrium. The imaginary part of the proposed spin Hamiltonian describes the\neffects of Gilbert damping and applied Slonczewski spin-transfer torque. In the\nclassical limit, our approach reproduces Landau-Lifshitz-Gilbert-Slonczewski\ndynamics of a large macrospin. We reveal the spin-transfer torque-driven\nparity-time symmetry-breaking phase transition corresponding to a transition\nfrom precessional to exponentially damped spin dynamics. Micromagnetic\nsimulations for nanoscale ferromagnetic disks demonstrate the predicted effect.\nOur findings can pave the way to a general quantitative description of\nout-of-equilibrium phase transitions driven by spontaneous parity-time symmetry\nbreaking.", "category": "cond-mat_other" }, { "text": "X-ray imaging of the dynamic magnetic vortex core deformation: Magnetic platelets with a vortex configuration are attracting considerable\nattention. The discovery that excitation with small in-plane magnetic fields or\nspin polarised currents can switch the polarisation of the vortex core did not\nonly open the possibility of using such systems in magnetic memories, but also\ninitiated the fundamental investigation of the core switching mechanism itself.\nMicromagnetic models predict that the switching is mediated by a\nvortex-antivortex pair, nucleated in a dynamically induced vortex core\ndeformation. In the same theoretical framework, a critical core velocity is\npredicted, above which switching occurs. Although these models are extensively\nstudied and generally accepted, experimental support has been lacking until\nnow. In this work, we have used high-resolution time-resolved X-ray microscopy\nto study the detailed dynamics in vortex structures. We could reveal the\ndynamic vortex core deformation preceding the core switching. Also, the\nthreshold velocity could be measured, giving quantitative comparison with\nmicromagnetic models.", "category": "cond-mat_other" }, { "text": "Ultracold Molecule Production Via a Resonant Oscillating Magnetic Field: A novel atom-molecule conversion technique has been investigated. Ultracold\n85Rb atoms sitting in a DC magnetic field near the 155G Feshbach resonance are\nassociated by applying a small sinusoidal oscillation to the magnetic field.\nThere is resonant atom to molecule conversion when the modulation frequency\nclosely matches the molecular binding energy. We observe that the atom to\nmolecule conversion efficiency depends strongly on the frequency, amplitude,\nand duration of the applied modulation and on the initial phase space density\nof the sample. This technique offers high conversion efficiencies without the\nnecessity of crossing or closely approaching the Feshbach resonance and allows\nprecise spectroscopic measurements.", "category": "cond-mat_other" }, { "text": "Stable and unstable vector dark solitons of coupled nonlinear\n Schr\u00f6dinger equations. Application to two-component Bose-Einstein\n condensates: Dynamics of vector dark solitons in two-component Bose-Einstein condensates\nis studied within the framework of the coupled one-dimensional nonlinear\nSchr\\\"odinger (NLS) equations. We consider the small amplitude limit in which\nthe coupled NLS equations are reduced to the coupled Korteweg-de Vries (KdV)\nequations. For a specific choice of the parameters the obtained coupled KdV\nequations are exactly integrable. We find that there exist two branches of\n(slow and fast) dark solitons corresponding to the two branches of the sound\nwaves. Slow solitons, corresponding to the lower branch of the acoustic wave\nappear to be unstable and transform during the evolution into the stable fast\nsolitons (corresponding to the upper branch of the dispersion law). Vector dark\nsolitons of arbitrary depths are studied numerically. It is shown that\neffectively different parabolic traps, to which the two components are\nsubjected, cause instability of the solitons leading to splitting of their\ncomponents and subsequent decay. Simple phenomenological theory, describing\noscillations of vector dark solitons in a magnetic trap is proposed.", "category": "cond-mat_other" }, { "text": "A strongly interacting Bose gas: Nozi\u00e8res and Schmitt-Rink theory and\n beyond: We calculate the critical temperature for Bose-Einstein condensation in a gas\nof bosonic atoms across a Feshbach resonance, and show how medium effects at\nnegative scattering lengths give rise to pairs reminiscent of the ones\nresponsible for fermionic superfluidity. We find that the formation of pairs\nleads to a large suppression of the critical temperature. Within the formalism\ndeveloped by Nozieres and Schmitt-Rink the gas appears mechanically stable\nthroughout the entire crossover region, but when interactions between pairs are\ntaken into account we show that the gas becomes unstable close to the critical\ntemperature. We discuss prospects of observing these effects in a gas of\nultracold Cs133 atoms where recent measurements indicate that the gas may be\nsufficiently long-lived to explore the many-body physics around a Feshbach\nresonance.", "category": "cond-mat_other" }, { "text": "Exploring correlated 1D Bose gases from the superfluid to the\n Mott-insulator state by inelastic light scattering: We report the Bragg spectroscopy of interacting one-dimensional Bose gases\nloaded in optical lattices across the superfluid to Mott-insulator phase\ntransition. Elementary excitations are created with a non-zero momentum and the\nresponse of the correlated 1D gases is in the linear regime. The complexity of\nthe strongly correlated quantum phases is directly displayed in the spectra\nwhich exhibit novel features. This work paves the way for a precise\ncharacterization of the state of correlated atomic phases in optical lattices.", "category": "cond-mat_other" }, { "text": "Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope: We present a detailed modeling and characterization of our scalable microwave\nnanoprobe, which is a micro-fabricated cantilever-based scanning microwave\nprobe with separated excitation and sensing electrodes. Using finite-element\nanalysis, the tip-sample interaction is modeled as small impedance changes\nbetween the tip electrode and the ground at our working frequencies near 1GHz.\nThe equivalent lumped elements of the cantilever can be determined by\ntransmission line simulation of the matching network, which routes the\ncantilever signals to 50 Ohm feed lines. In the microwave electronics, the\nbackground common-mode signal is cancelled before the amplifier stage so that\nhigh sensitivity (below 1 atto-Farad capacitance changes) is obtained.\nExperimental characterization of the microwave probes was performed on\nion-implanted Si wafers and patterned semiconductor samples. Pure electrical or\ntopographical signals can be realized using different reflection modes of the\nprobe.", "category": "cond-mat_other" }, { "text": "Universal Relations of Energy Flow, Acoustic Spin and Torque for\n Near-Field Acoustic Tweezers: Acoustic spin, radiation torque, energy flow, and reactive power are of\nsignificant importance from both fundamental and practical aspects, responsible\nfor flexible tweezer manipulations and near-field sound directionality.\nNevertheless, the intrinsic relations among these physical quantities are far\nfrom clear. Here, we prove the universal geometric relations among them in\nacoustics, independent on wave structure details. Particularly, we connect\nacoustic spin and torque to the cross product of time-averaged energy flow and\nreactive power, as well as to the local vorticity of energy flow. These\nrelations are universally valid, verified in a variety of different acoustic\nsystems. We also demonstrate the multipole mechanical torques and forces\ngenerated in three acoustic near-field sources: Janus, Huygens and Spin\nsources, applying on small lossy particles. These universal geometric relations\nuncover hidden locking relations beyond simple spin-momentum locking of\nnear-field waves, and show the basic principles between the acoustic spin,\nradiation torque, and energy flow, reactive power.", "category": "cond-mat_other" }, { "text": "Quantum control and entanglement using periodic driving fields: We propose a scheme for producing directed motion in a lattice system by\napplying a periodic driving potential. By controlling the dynamics by means of\nthe effect known as coherent destruction of tunneling, we demonstrate a novel\nratchet-like effect that enables particles to be coherently manipulated and\nsteered without requiring local control. Entanglement between particles can\nalso be controllably generated, which points to the attractive possibility of\nusing these technique for quantum information processing.", "category": "cond-mat_other" }, { "text": "Quantum depletion of collapsing Bose-Einstein condensates: We perform the first numerical three-dimensional studies of quantum field\neffects in the Bosenova experiment on collapsing condensates by E. Donley et\nal. [Nature 415, 39 (2002)] using the exact experimental geometry. In a\nstochastic truncated Wigner simulation of the collapse, the collapse times are\nlarger than the experimentally measured values. We find that a finite\ntemperature initial state leads to an increased creation rate of uncondensed\natoms, but not to a reduction of the collapse time. A comparison of the\ntime-dependent Hartree-Fock-Bogoliubov and Wigner methods for the more\ntractable spherical trap shows excellent agreement between the uncondensed\npopulations. We conclude that the discrepancy between the experimental and\ntheoretical values of the collapse time cannot be explained by Gaussian quantum\nfluctuations or finite temperature effects.", "category": "cond-mat_other" }, { "text": "Superfluid behavior of quasi-1D p-H$_2$ inside carbon nanotube: We perform ab-initio Quantum Monte Carlo simulations of para-hydrogen\n(pH$_2$) at $T=0$ K confined in carbon nanotubes (CNT) of different radii. The\nradial density profiles show a strong layering of the pH$_2$ molecules which\ngrow, with increasing number of molecules, in solid concentric cylindrical\nshells and eventually a central column. The central column can be considered an\neffective one-dimensional (1D) fluid whose properties are well captured by the\nTomonaga-Luttinger liquid theory. The Luttinger parameter is explicitly\ncomputed and interestingly it shows a non-monotonic behavior with the linear\ndensity similar to what found for pure 1D $^3$He. Remarkably, for the central\ncolumn in a (10,10) CNT, we found an ample linear density range in which the\nLuttinger liquid is (i) superfluid and (ii) stable against a weak disordered\nexternal potential, as the one expected inside realistic pores. This superfluid\nbehavior could be experimentally revealed in bundles of carbon nanotubes, where\ndeviations from classical inertial values associated with superfluid density\ncould be measured via torsional oscillator techniques. In summary, our results\nsuggest that pH$_2$ within carbon nanopores could be a practical realization of\nthe long sought-after, elusive superfluid phase of parahydrogen.", "category": "cond-mat_other" }, { "text": "Stability of the decagonal quasicrystal in the Lennard-Jones-Gauss\n system: Although quasicrystals have been studied for 25 years, there are many open\nquestions concerning their stability: What is the role of phason fluctuations?\nDo quasicrystals transform into periodic crystals at low temperature? If yes,\nby what mechanisms? We address these questions here for a simple\ntwo-dimensional model system, a monatomic decagonal quasicrystal, which is\nstabilized by the Lennard-Jones-Gauss potential in thermodynamic equilibrium.\nIt is known to transform to the approximant Xi, when cooled below a critical\ntemperature. We show that the decagonal phase is an entropically stabilized\nrandom tiling. By determining the average particle energy for a series of\napproximants, it is found that the approximant Xi is the one with lowest\npotential energy.", "category": "cond-mat_other" }, { "text": "Study of superfluid $^3$He under nanoscale confinement. A new approach\n to the investigation of superfluid $^3$He films: We review recent experiments in which superfluid $^3$He has been studied\nunder highly controlled confinement in nanofluidic sample chambers. We discuss\nthe experimental challenges and their resolution. These methods open the way to\na systematic investigation of the superfluidity of $^3$He films, and the\nsurface and edge excitations of topological superfluids.", "category": "cond-mat_other" }, { "text": "Creating stable molecular condensate using a generalized Raman adiabatic\n passage scheme: We study the Feshbach resonance assisted stimulated adiabatic passage of an\neffective coupling field for creating stable molecules from atomic Bose\ncondensate. By exploring the properties of the coherent population trapping\nstate, we show that, contrary to the previous belief, mean-field shifts need\nnot to limit the conversion efficiency as long as one chooses an adiabatic\npassage route that compensates the collision mean-field phase shifts and avoids\nthe dynamical unstable regime.", "category": "cond-mat_other" }, { "text": "Finite Temperature Dynamics of Spin Solitons with Applications in\n Thermocouples and Refrigerators: The exploitation of spin Berry phases to generate emergent fields for\nproducing miniaturized and high-quality inductors has enjoyed considerable\npopularity among proponents of quantum technologies [Nature 586, 202 (2020)}].\nInspired by this breakthrough, we extend its mechanism to spin thermoelectrics\nby probing responses of ferrimagnetic domain walls (DWs) to thermal gradients.\nSimilarly, voltages here stem from DW-spin collective motion, in contrast to\nnormal electron transport phenomena. We further develop finite-temperature\ndynamics to investigate thermoelectric figures of merit and attribute\ncorresponding quantum superiority to ultrafast spin evolution of ferrimagnetism\nwith tunable non-Abelian phases. We propose a more likely cause of DW motion\ntowards hot or cold regions (contrary to conclusions of previous reports) and\nverify existence of efficient magnon-momentum transfers. These findings deepen\nour understanding of heat-driven DW kinetics and suggest profitable new\ndirections in an emerging realm of spincaloritronics.", "category": "cond-mat_other" }, { "text": "Superfluid shells for trapped fermions with mass and population\n imbalance: We map out the phase diagram of strongly interacting fermions in a potential\ntrap with mass and population imbalance between the two spin components. As a\nunique feature distinctively different from the equal-mass case, we show that\nthe superfluid here forms a shell structure which is not simply connected in\nspace. Different types of normal states occupy the trap regions inside and\noutside this superfluid shell. We calculate the atomic density profiles, which\nprovide an experimental signature for the superfluid shell structure.", "category": "cond-mat_other" }, { "text": "Symbiotic Solitons in Heteronuclear Multicomponent Bose-Einstein\n condensates: We show that bright solitons exist in quasi-one dimensional heteronuclear\nmulticomponent Bose-Einstein condensates with repulsive self-interaction and\nattractive inter-species interaction. They are remarkably robust to\nperturbations of initial data and collisions and can be generated by the\nmechanism of modulational instability. Some possibilities for control and the\nbehavior of the system in three dimensions are also discussed.", "category": "cond-mat_other" }, { "text": "Virial theorems for trapped cold atoms: We present a general virial theorem for quantum particles with arbitrary\nzero-range or finite-range interactions in an arbitrary external potential. We\ndeduce virial theorems for several situations relevant to trapped cold atoms:\nzero-range interactions with and without Efimov effect, hard spheres, narrow\nFeshbach resonances, and finite-range interactions. If the scattering length\n$a$ is varied adiabatically in the BEC-BCS crossover, we find that the trapping\npotential energy as a function of $1/a$ has an inflexion point at unitarity.", "category": "cond-mat_other" }, { "text": "Effect of fluctuations on the superfluid-supersolid phase transition on\n the lattice: We derive a controlled expansion into mean field plus fluctuations for the\nextended Bose-Hubbard model, involving interactions with many neighbors on an\narbitrary periodic lattice, and study the superfluid-supersolid phase\ntransition. Near the critical point, the impact of (thermal and quantum)\nfluctuations on top of the mean field grows, which entails striking effects,\nsuch as negative superfluid densities and thermodynamical instability of the\nsuperfluid phase -- earlier as expected from mean-field dynamics. We also\npredict the existence of long-lived \"supercooled\" states with anomalously large\nquantum fluctuations.", "category": "cond-mat_other" }, { "text": "Probing the intrinsic state of a one-dimensional quantum well with a\n photon-assisted tunneling: The photon-assisted tunneling (PAT) through a single wall carbon nanotube\nquantum well (QW) under influence an external electromagnetic field for probing\nof the Tomonaga Luttinger liquid (TLL) state is suggested. The elementary TLL\nexcitations inside the quantum well are density ($\\rho_{\\pm}$) and spin\n($\\sigma_{\\pm} $) bosons. The bosons populate the quantized energy levels\n$\\epsilon^{\\rho +}_n =\\Delta n/ g$ and $\\epsilon^{\\rho -(\\sigma \\pm)}_n =\n\\Delta n$ where $\\Delta = h v_F /L $ is the interlevel spacing, $n$ is an\ninteger number, $L$ is the tube length, $g$ is the TLL parameter. Since the\nelectromagnetic field acts on the $\\rho_{+}$ bosons only while the neutral\n$\\rho_{-}$ and $\\sigma_{\\pm} $ bosons remain unaffected, the PAT spectroscopy\nis able of identifying the $\\rho_{+}$ levels in the QW setup. The spin\n$\\epsilon_n^{\\sigma+} $ boson levels in the same QW are recognized from Zeeman\nsplitting when applying a d.c. magnetic field $H \\neq 0$ field. Basic TLL\nparameters are readily extracted from the differential conductivity curves.", "category": "cond-mat_other" }, { "text": "Ultracold atoms confined in an optical lattice plus parabolic potential:\n a closed-form approach: We discuss interacting and non-interacting one dimensional atomic systems\ntrapped in an optical lattice plus a parabolic potential. We show that, in the\ntight-binding approximation, the non-interacting problem is exactly solvable in\nterms of Mathieu functions. We use the analytic solutions to study the\ncollective oscillations of ideal bosonic and fermionic ensembles induced by\nsmall displacements of the parabolic potential. We treat the interacting boson\nproblem by numerical diagonalization of the Bose-Hubbard Hamiltonian. From\nanalysis of the dependence upon lattice depth of the low-energy excitation\nspectrum of the interacting system, we consider the problems of\n\"fermionization\" of a Bose gas, and the superfluid-Mott insulator transition.\nThe spectrum of the noninteracting system turns out to provide a useful guide\nto understanding the collective oscillations of the interacting system,\nthroughout a large and experimentally relevant parameter regime.", "category": "cond-mat_other" }, { "text": "Full counting statistics of heteronuclear molecules from\n Feshbach-assisted photo association: We study the effects of quantum statistics on the counting statistics of\nultracold heteronuclear molecules formed by Feshbach-assisted photoassociation\n[Phys. Rev. Lett. {\\bf 93}, 140405 (2004)]. Exploiting the formal similarities\nwith sum frequency generation and using quantum optics methods we consider the\ncases where the molecules are formed from atoms out of two Bose-Einstein\ncondensates, out of a Bose-Einstein condensate and a gas of degenerate\nfermions, and out of two degenerate Fermi gases with and without superfluidity.\nBosons are treated in a single mode approximation and fermions in a degenerate\nmodel. In these approximations we can numerically solve the master equations\ndescribing the system's dynamics and thus we find the full counting statistics\nof the molecular modes. The full quantum dynamics calculations are complemented\nby mean field calculations and short time perturbative expansions. While the\nmolecule production rates are very similar in all three cases at this level of\napproximation, differences show up in the counting statistics of the molecular\nfields. The intermediate field of closed-channel molecules is for short times\nsecond-order coherent if the molecules are formed from two Bose-Einstein\ncondensates or a Bose-Fermi mixture. They show counting statistics similar to a\nthermal field if formed from two normal Fermi gases. The coherence properties\nof molecule formation in two superfluid Fermi gases are intermediate between\nthe two previous cases. In all cases the final field of deeply-bound molecules\nis found to be twice as noisy as that of the intermediate state. This is a\nconsequence of its coupling to the lossy optical cavity in our model, which\nacts as an input port for quantum noise, much like the situation in an optical\nbeam splitter.", "category": "cond-mat_other" }, { "text": "Electric power transfer in spin pumping experiments: Spin pumping is becoming an established method to generate voltages from\nmagnetic dynamics. The standard detection method of spin pumping is based on\nopen circuit voltage measurement across ferromagnetic (FM) and non-magnetic\n(NM) bi-layers, where the inverse spin-Hall effect (ISHE) can convert spin\ncurrents into electrical charge accumulation. In this paper, we present that it\nis also possible to measure the associated electric charge current generated in\nFM/NM bi-layers, by using a macroscopic closed circuitry detection method.\nUsing variable load resistors connected in series to the sample, we quantified\ncharge currents and associated electric power dissipation as a function of the\nload resistance. By using basic circuit analysis, we are able to describe spin\npumping cells as a non-ideal voltage source or equivalent current source with\nan internal resistor.", "category": "cond-mat_other" }, { "text": "The absence of fragmentation in Bose-Einstein condensates: A Bose-Einstein condensate produced by a Hamiltonian which is rotationally or\ntranslationally symmetric is fragmented as a direct result of these symmetries.\nA corresponding mean-field unfragmented state, with an identical energy to\nleading order in the number of particles, can generally be constructed. As a\nconsequence, vanishingly weak symmetry-breaking perturbations destabilize the\nfragmented state, which would thus be extremely difficult to realize\nexperimentally, and lead to an unfragmented condensate.", "category": "cond-mat_other" }, { "text": "Possible experiment for determination of the role of microscopic vortex\n rings in the \u03bb-transition in He-II: It is suggested that microscopic vortex rings (MVR) play an important role in\nthe \\lambda-transition in helium-II and substantially determine the value of\nT_{\\lambda}. For very thin films of He-II, with thickness d less than the size\nof the smallest MVR, the rings do not fit in and, therefore, do not exist in\nsuch films. Consequently, for superfluid films of He-II, a peculiarity in the\nform of a smoothed-out jump should be observed in the curve T_{m}(d) at the\nvalues of thickness approximately equal to the size of the smallest MVR, d= 3 -\n9 A (T_{m} is the temperature of the maximum of the broad peak on the curve of\nthe dependence of the specific heat on temperature). The absence of a similar\npeculiarity will be an evidence that MVR do not influence the values of\nT_{\\lambda} and T_{m}, and do not play any key role in the \\lambda-transition.\nThe currently available experimental data are insufficient for revealing the\npredicted peculiarity.", "category": "cond-mat_other" }, { "text": "Phase diagram for a Bose-Einstein condensate moving in an optical\n lattice: The stability of superfluid currents in a system of ultracold bosons was\nstudied using a moving optical lattice. Superfluid currents in a very weak\nlattice become unstable when their momentum exceeds 0.5 recoil momentum.\nSuperfluidity vanishes already for zero momentum as the lattice deep reaches\nthe Mott insulator(MI) phase transition. We study the phase diagram for the\ndisappearance of superfluidity as a function of momentum and lattice depth\nbetween these two limits. Our phase boundary extrapolates to the critical\nlattice depth for the superfluid-to-MI transition with 2% precision. When a\none-dimensional gas was loaded into a moving optical lattice a sudden\nbroadening of the transition between stable and unstable phases was observed.", "category": "cond-mat_other" }, { "text": "Endurance Write Speed Tradeoffs in Nonvolatile Memories: We derive phenomenological model for endurance-write time switching tradeoff\nfor nonvolatile memories with thermally activated switching mechanisms. The\nmodel predicts linear to cubic dependence of endurance on write time for metal\noxide memristors and flash memories, which is partially supported by\nexperimental data for the breakdown of metal-oxide thin films.", "category": "cond-mat_other" }, { "text": "A Tonks Giradeau Gas in the Presence of a Local Potential: The physics of a Tonks-Giradeau Gas in the presence of a local potential is\nstudied. In order to evaluate the single particle density matrix (SPDM) of the\nmany-body ground state, the Wiger-Jordan transformation is used. The\neigenvector with the largest eigenvalue of the SPDM corresponds to the\n\"Bose-Einstein Condensate\"(BEC) State. We find that the \"BEC\" state density at\nthe positon of the local potential decreases, as expected, in the case of a\nrepulsive potential. For an attractive potential, it decreases or increases\ndepending on the strength of the potential. The superfluidity of this system is\ninvestigated both numerically and perturbatively. An experimental method for\ndetecting the effect of an impurity in a Tonks-Giradueau gas is discussed.", "category": "cond-mat_other" }, { "text": "Topologically trapped vortex molecules in Bose-Einstein condensates: In a numerical experiment based on Gross-Pitaevskii formalism, we demonstrate\nunique topological quantum coherence in optically trapped Bose-Einstein\ncondensates (BECs). Exploring the fact that vortices in rotating BEC can be\npinned by a geometric arrangement of laser beams, we show the parameter range\nin which vortex-antivortex molecules or multiquantum vortices are formed as a\nconsequence of the optically imposed symmetry. Being low-energy states, we\ndiscuss the conditions for spontaneous nucleation of these unique molecules and\ntheir direct experimental observation, and provoke the potential use of the\nphase print of an antivortex or a multiquantum vortex when realized in\nunconventional circumstances.", "category": "cond-mat_other" }, { "text": "Equation of state of cubic boron nitride at high pressures and\n temperatures: We report accurate measurements of the equation of state (EOS) of cubic boron\nnitride by x-ray diffraction up to 160 GPa at 295 K and 80 GPa in the range\n500-900 K. Experiments were performed on single-crystals embedded in a\nquasi-hydrostatic pressure medium (helium or neon). Comparison between the\npresent EOS data at 295 K and literature allows us to critically review the\nrecent calibrations of the ruby standard. The full P-V-T data set can be\nrepresented by a Mie-Gr\\\"{u}neisen model, which enables us to extract all\nrelevant thermodynamic parameters: bulk modulus and its first\npressure-derivative, thermal expansion coefficient, thermal Gr\\\"{u}neisen\nparameter and its volume dependence. This equation of state is used to\ndetermine the isothermal Gr\\\"{u}neisen mode parameter of the Raman TO band. A\nnew formulation of the pressure scale based on this Raman mode, using\nphysically-constrained parameters, is deduced.", "category": "cond-mat_other" }, { "text": "The Plastic Flow of Solid 4He through a Porous Membrane: The flow velocity of solid 4He through a porous membrane frozen into a\ncrystal has been measured in the temperature interval 0.1 - 1.8 K. A flat\ncapacitor consisting of a metalized plastic porous membrane and a bulk\nelectrode is applied and the gap in the capacitor was filled with examined\nhelium. The flow of helium through the membrane pores is caused by a d.c.\nvoltage applied to the capacitor plates. Above T~1K the velocity of solid 4He\nflow decreases with lowering temperature following the Arrhenius law with the\nactivation energy of the process closed to that of vacancies. At low\ntemperatures the velocity is practically independent of temperature, which\nsuggests a transition in 4He from the classical thermally activated\nvacancy-related flow to the quantum plastic flow.", "category": "cond-mat_other" }, { "text": "Dynamics of matter-wave and optical fields in superradiant scattering\n from Bose-Einstein condensates: We study superradiant scattering off Bose-Einstein condensates by solving the\nsemiclassical Maxwell-Schroedinger equations describing the coupled dynamics of\nmatter-wave and optical fields. Taking the spatial dependence of these fields\nalong the condensate axis into account, we are able to reproduce and explain\nmany of the characteristic features observed in the experiments of Inouye et\nal. [Science 285, 571 (1999)] and Schneble et al. [Science 300, 475 (2003)],\nsuch as the shape of the atomic side-mode distributions for forward and\nbackward scattering, the spatial asymmetry between forward and backward side\nmodes, and the depletion of the condensate center observed for forward\nscattering.", "category": "cond-mat_other" }, { "text": "Long-range correlation energies and off-diagonal interactions for the\n $\u03c0$ electronic systems: The long-range correlation energies and the off-diagonal interactions are\nstudied and a general formula for correlation energy $E_c$ of the $\\pi$\nelectron systems is given, which is beyond the nearest-neighbor\nelectron-electron interactions and includes the off-diagonal interactions. It\nis found that the effects of the off-diagonal interactions $W$ and $X$ on the\ncorrelation energies are opposite, but the influence of $X$ on the correlation\nenergies is much stronger than that of $W$ on the correlation energies, and the\ncorrelation energies decrease with increasing the screening effect.", "category": "cond-mat_other" }, { "text": "Critical temperature of a trapped Bose gas: comparison of theory and\n experiment: We apply the Projected Gross-Pitaevskii equation (PGPE) formalism to the\nexperimental problem of the shift in critical temperature $T_c$ of a\nharmonically confined Bose gas as reported in Gerbier \\emph{et al.} [Phys. Rev.\nLett. \\textbf{92}, 030405 (2004)]. The PGPE method includes critical\nfluctuations and we find the results differ from various mean-field theories,\nand are in best agreement with experimental data. To unequivocally observe\nbeyond mean-field effects, however, the experimental precision must either\nimprove by an order of magnitude, or consider more strongly interacting\nsystems. This is the first application of a classical field method to make\nquantitative comparison with experiment.", "category": "cond-mat_other" }, { "text": "Low-energy effective theory of the toric code model in a parallel field: We determine analytically the phase diagram of the toric code model in a\nparallel magnetic field which displays three distinct regions. Our study relies\non two high-order perturbative expansions in the strong- and weak-field limit,\nas well as a large-spin analysis. Calculations in the topological phase\nestablish a quasiparticle picture for the anyonic excitations. We obtain two\nsecond-order transition lines that merge with a first-order line giving rise to\na multicritical point as recently suggested by numerical simulations. We\ncompute the values of the corresponding critical fields and exponents that\ndrive the closure of the gap. We also give the one-particle dispersions of the\nanyonic quasiparticles inside the topological phase.", "category": "cond-mat_other" }, { "text": "Estimation of the spatial decoherence time in circular quantum dots: We propose a simple phenomenological model to estimate the spatial\ndecoherence time in quantum dots. The dissipative phase space dynamics is\ndescribed in terms of the density matrix and the corresponding Wigner function,\nwhich are derived from a master equation with Lindblad operators linear in the\ncanonical variables. The formalism was initially developed to describe\ndiffusion and dissipation in deep inelastic heavy ion collisions, but also an\napplication to quantum dots is possible. It allows us to study the dependence\nof the decoherence rate on the dissipation strength, the temperature and an\nexternal magnetic field, which is demonstrated in illustrative calculations on\na circular GaAs one-electron quantum dot.", "category": "cond-mat_other" }, { "text": "The Linear and Non-linear Magnetic Response of a Tri-Uranium Single\n Molecule Magnet: We report here low temperature magnetization isotherms for the single\nmolecule magnet, $(UO_2-L)_3$. By analyzing the low temperature magnetization\nin terms of $M= X_1*B + X_3*B^3$ we extract the linear susceptibility $X_1$ and\nthe leading order nonlinear susceptibility $X_3$. We find that $X_1$ exhibits a\npeak at a temperature of $T_1=10.4 K$ with $Chi_3$ also exhibiting a peak but\nat a reduced temperature $T3 = 5 K$. At the lowest temperatures the isotherms\nexhibit a critical field $B_c = 11.5 T$ marked by a clear point of inflection.\nA minimal Hamiltonian employing S=1 (pseudo) spins with only a single energy\nscale (successfully used to model the behavior of bulk f-electron metamagnets)\nis shown to provide a good description of the observed linear scaling between\n$T_1, T_3$ and $B_c$. We further show that a Heisenberg Hamiltonian previously\nemployed by Carretta et al. (2013 J. Phys.Cond. Matt. 25 486001) to model this\nsingle molecule magnet gives formulas for the angle averaged susceptibilities\n(in the Ising limit) very similar to those of the minimal model.", "category": "cond-mat_other" }, { "text": "Adiabatic Transport of Bose-Einstein Condensate in Double- and\n Triple-Well Traps: By using a close similarity between multi-photon and tunneling population\ntransfer schemes, we propose robust adiabatic methods for the transport of\nBose-Einstein condensate (BEC) in double- and triple-well traps. The\ncalculations within the mean-field approximation (Gross-Pitaevskii equation)\nshow that irreversible and complete transport takes place even in the presence\nof the non-linear effects caused by interaction between BEC atoms. The transfer\nis driven by adiabatic time-dependent monitoring the barriers and well depths.\nThe proposed methods are universal and can be applied to a variety of systems\nand scenarios.", "category": "cond-mat_other" }, { "text": "Applying matrix product operators to model systems with long-range\n interactions: An algorithm is presented which computes a translationally invariant matrix\nproduct state approximation of the ground state of an infinite 1D system; it\ndoes this by embedding sites into an approximation of the infinite\n``environment'' of the chain, allowing the sites to relax, and then merging\nthem with the environment in order to refine the approximation. By making use\nof matrix product operators, our approach is able to directly model any\nlong-range interaction that can be systematically approximated by a series of\ndecaying exponentials. We apply our techniques to compute the ground state of\nthe Haldane-Shastry model and present results.", "category": "cond-mat_other" }, { "text": "S-mixing and quantum tunneling of the magnetization in molecular\n nanomagnets: The role of $S$-mixing in the quantum tunneling of the magnetization in\nnanomagnets has been investigated. We show that the effect on the tunneling\nfrequency is huge and that the discrepancy (more than 3 orders of magnitude in\nthe tunneling frequency) between spectroscopic and relaxation measurements in\nFe$_8$ can be resolved if $S$-mixing is taken into account.", "category": "cond-mat_other" }, { "text": "Electron sound in metals: This paper is devoted to the investigation of electron sound -- oscillations\nof the electron distribution function coupled with elastic deformation and\npropagating with the Fermi velocity. The amplitude-phase relations\ncharacterizing the behavior of the electron sound in Ga single crystals are\ndetermined experimentally. A model problem of excitation of electron sound in a\ncompensated metal with equivalent bands is solved for a finite sample with\ndiffusive scattering of electrons at the interfaces. It was found that the\ndisplacement amplitude of the receiving interface is two orders of magnitude\nlarger than the elastic amplitude of the wave due to electron pressure. It was\nestablished that the changes occurring in the amplitude and phase of the\nelectron sound waves at a superconducting transition do not depend on the path\ntraversed by the wave, i.e. they refer only to the behavior of the\ntransformation coefficient.", "category": "cond-mat_other" }, { "text": "Full transmission through perfect-conductor subwavelength hole arrays: Light transmission through 2D subwavelength hole arrays in perfect-conductor\nfilms is shown to be complete (100%) at some resonant wavelengths even for\narbitrarily narrow holes. Conversely, the reflection on a 2D planar array of\nnon-absorbing scatterers is shown to be complete at some wavelengths regardless\nhow weak the scatterers are. These results are proven analytically and\ncorroborated by rigorous numerical solution of Maxwell's equations. This work\nsupports the central role played by dynamical diffraction during light\ntransmission through subwavelength hole arrays and it provides a systematics to\nanalyze more complex geometries and many of the features observed in connection\nwith transmission through hole arrays.", "category": "cond-mat_other" }, { "text": "Entanglement and errors in the control of spins by optical coupling: We analyze the optical quantum control of impurity spins in proximity to a\nquantum dot. A laser pulse creates an exciton in the dot and controls the spins\nby indirect coupling. We show how to determine the control parameters using as\nan illustration the production of maximal spin entanglement. We consider errors\nin the quantum control due to the exciton radiative recombination. The control\nerrors in the adiabatic and nonadiabatic case are compared to the threshold\nneeded for scalable quantum computing.", "category": "cond-mat_other" }, { "text": "Photoinduced vibronic coupling in two-level dissipative systems: Interaction of an electron system with a strong electromagnetic wave leads to\nrearrangement both the electron and vibrational energy spectra of a dissipative\nsystem. For instance, the optically coupled electron levels become split in the\nconditions of the ac Stark effect that gives rise to appearance of the\nnonadiabatic coupling between the electron and vibrational motions. The\nnonadiabatic coupling exerts a substantial impact on the electron and phonon\ndynamics and must be taken into account to determine the system wave functions.\nIn this paper, the vibronic coupling induced by the ac Stark effect is\nconsidered. It is shown that the interaction between the electron states\ndressed by an electromagnetic field and the forced vibrations of reservoir\noscillators under the action of rapid changing of the electron density with the\nRabi frequency is responsible for establishment of the photoinduced vibronic\ncoupling. However, if the resonance conditions for the optical phonon frequency\nand the transition frequency of electrons in the dressed state basis are\nsatisfied, the vibronic coupling is due to the electron-phonon interaction.\nAdditionally, photoinduced vibronic coupling results in appearance of the\ndoubly dressed states which are formed by both the electron-photon and\nelectron-vibrational interactions.", "category": "cond-mat_other" }, { "text": "Continuum Mechanics for Quantum Many-Body Systems: The Linear Response\n Regime: We derive a closed equation of motion for the current density of an\ninhomogeneous quantum many-body system under the assumption that the\ntime-dependent wave function can be described as a geometric deformation of the\nground-state wave function. By describing the many-body system in terms of a\nsingle collective field we provide an alternative to traditional approaches,\nwhich emphasize one-particle orbitals. We refer to our approach as continuum\nmechanics for quantum many-body systems. In the linear response regime, the\nequation of motion for the displacement field becomes a linear fourth-order\nintegro-differential equation, whose only inputs are the one-particle density\nmatrix and the pair correlation function of the ground-state. The complexity of\nthis equation remains essentially unchanged as the number of particles\nincreases. We show that our equation of motion is a hermitian eigenvalue\nproblem, which admits a complete set of orthonormal eigenfunctions under a\nscalar product that involves the ground-state density. Further, we show that\nthe excitation energies derived from this approach satisfy a sum rule which\nguarantees the exactness of the integrated spectral strength. Our formulation\nbecomes exact for systems consisting of a single particle, and for any\nmany-body system in the high-frequency limit. The theory is illustrated by\nexplicit calculations for simple one- and two-particle systems.", "category": "cond-mat_other" }, { "text": "Evolution of Electronic and Vibrational Polarity of NaF Nanocrystals\n from Diatomic to Bulk: A Density Functional Study: Density functional theory (DFT) is used to study vibrations, electrical\ndipole moments, and polarizabilities of NaF clusters. Because of prior\nexperimental and theoretical studies, this is a good model system for tracking\nthe evolution of the properties from diatomic molecule to bulk crystal. The\nratio of vibrational to electronic contributions to the polarizability\nincreases dramatically with size N in the closed shell clusters (NaF)_N. The\nopen shell system Na_14F_13 has a greatly enhanced electronic polarizability.\nContrary to previous studies on this system which treated only the outer\nelectron by quantum mechanics, we find the O_h cubic structure to be stable\nrelative to the polar distorted structures such as C_3v.", "category": "cond-mat_other" }, { "text": "On non-markovian nature of stock trading: Using a relationship between the moments of the probability distribution of\ntimes between the two consecutive trades (intertrade time distribution) and the\nmoments of the distribution of a daily number of trades we show, that the\nunderlying point process generating times of the trades is an essentially\nnon-markovian long-range memory one. Further evidence for the long-range memory\nnature of this point process is provided by the powerlike correlation between\nthe intertrade time intervals. The data set includes all trades in EESR stock\non the Moscow International Currency Exchange in January 2003 - September 2003\nand in Siemens, Commerzbank and Karstadt stocks traded on the Xetra electronic\nstock exchange of Deutsche Boerse in October 2002.", "category": "cond-mat_other" }, { "text": "Manifolds of quasi-constant SOAP and ACSF fingerprints and the resulting\n failure to machine learn four-body interactions: Atomic fingerprints are commonly used for the characterization of local\nenvironments of atoms in machine learning and other contexts. In this work, we\nstudy the behavior of two widely used fingerprints, namely the smooth overlap\nof atomic positions (SOAP) and the atom-centered symmetry functions (ACSF),\nunder finite changes of atomic positions and demonstrate the existence of\nmanifolds of quasi-constant fingerprints. These manifolds are found numerically\nby following eigenvectors of the sensitivity matrix with quasi-zero\neigenvalues. The existence of such manifolds in ACSF and SOAP causes a failure\nto machine learn four-body interactions such as torsional energies that are\npart of standard force fields. No such manifolds can be found for the Overlap\nMatrix (OM) fingerprint due to its intrinsic many-body character.", "category": "cond-mat_other" }, { "text": "Possible display of phason mode of electromagnons in TbMnO3: The interaction of light in terahertz frequency region with electromagnons in\na sinusoidal incommensurate magnetic state in TbMnO3 is studied. A significant\nchange in the frequency dependence of the dielectric constant e_zz near the\ntemperature of the phase transition from sinusoidal magnetic ordering to spiral\nspin structure with a spontaneous electric poiarization is predicted. Phason\nmode of this phase transition is the mode of electromagnon with ME coupling\nproportional to the wave number of modulation structure.", "category": "cond-mat_other" }, { "text": "Dynamical Instability of a Doubly Quantized Vortex in a Bose-Einstein\n condensate: Doubly quantized vortices were topologically imprinted in $|F=1>$ $^{23}$Na\ncondensates, and their time evolution was observed using a tomographic imaging\ntechnique. The decay into two singly quantized vortices was characterized and\nattributed to dynamical instability. The time scale of the splitting process\nwas found to be longer at higher atom density.", "category": "cond-mat_other" }, { "text": "Stability and excitations of solitons in 2D Bose-Einstein condensates: The small oscillations of solitons in 2D Bose-Einstein condensates are\ninvestigated by solving the Kadomtsev-Petviashvili equation which is valid when\nthe velocity of the soliton approaches the speed of sound. We show that the\nsoliton is stable and that the lowest excited states obey the same dispersion\nlaw as the one of the stable branch of excitations of a 1D gray soliton in a 2D\ncondensate. The role of these states in thermodynamics is discussed.", "category": "cond-mat_other" }, { "text": "Sandpiles and superconductors: dual variational formulations for\n critical-state problems: Similar evolutionary variational inequalities appear as convenient\nformulations for continuous models for sandpile growth, magnetization of\ntype-II superconductors, and evolution of some other dissipative systems\ncharacterized by the multiplicity of metastable states, long-range\ninteractions, avalanches, and hysteresis. The origin of this similarity is that\nthese are quasistationary models of equilibrium in which the multiplicity of\nmetastable states is a consequence of a unilateral condition of equilibrium\n(critical-state constraint). Existing variational formulations for\ncritical-state models of sandpiles and superconductors are convenient for\nmodelling only the \"primary\" variables (evolving pile shape and magnetic field,\nrespectively). The conjugate variables (the surface sand flux and the electric\nfield) are also of interest in various applications. Here we derive dual\nvariational formulations, similar to mixed variational inequalities in\nplasticity, for the sandpile and superconductor models. These formulations are\nused in numerical simulations and allow us to approximate simultaneously both\nthe primary and dual variables.", "category": "cond-mat_other" }, { "text": "Discontinuities in fourth sound waves in superfluid helium: Formation of fourth-sound shock waves in narrow channels filled with\nsuperfluid helium is studied. Physical and mathematical conditions at the\nsurface of discontinuity are established. These conditions differ somewhat from\nthose in case of first- and second-sound waves. The velocity of discontinuity\ncoincides with that of fourth sound. The jumps of temperature and the\nsuperfluid velocity are shown to be of the first order as to the pressure\njumps.", "category": "cond-mat_other" }, { "text": "Inhibition of Transport of a Bose-Einstein Condensate in a Random\n Potential: We observe the suppression of the 1D transport of an interacting elongated\nBose-Einstein condensate in a random potential with a standard deviation small\ncompared to the typical energy per atom, dominated by the interaction energy.\nNumerical solutions of the Gross-Pitaevskii equation reproduce well our\nobservations. We propose a scenario for disorder-induced trapping of the\ncondensate in agreement with our observations.", "category": "cond-mat_other" }, { "text": "Aging in Citation Networks: In many growing networks, the age of the nodes plays an important role in\ndeciding the attachment probability of the incoming nodes. For example, in a\ncitation network, very old papers are seldom cited while recent papers are\nusually cited with high frequency. We study actual citation networks to find\nout the distribution $T(t)$ of $t$, the time interval between the published and\nthe cited paper. For different sets of data we find a universal behaviour:\n$T(t) \\sim t^{-0.9}$ for $t \\leq t_c$ and $T(t) \\sim t^{-2}$ for $t>t_c$ where\n$t_c \\sim O(10)$.", "category": "cond-mat_other" }, { "text": "Tunneling in a uniform one-dimensional superfluid: emergence of a\n complex instanton: In a uniform ring-shaped one-dimensional superfluid, quantum fluctuations\nthat unwind the order parameter need to transfer momentum to quasiparticles\n(phonons). We present a detailed calculation of the leading exponential factor\ngoverning the rate of such phonon-assisted tunneling in a weakly-coupled Bose\ngas at a low temperature $T$. We also estimate the preexponent. We find that\nfor small superfluid velocities the $T$-dependence of the rate is given mainly\nby $\\exp(-c_s P/ 2T)$, where $P$ is the momentum transfer, and $c_s$ is the\nphonon speed. At low $T$, this represents a strong suppression of the rate,\ncompared to the non-uniform case. As a part of our calculation, we identify a\ncomplex instanton, whose analytical continuation to suitable real-time segments\nis real and describes formation and decay of coherent quasiparticle states with\nnonzero total momenta.", "category": "cond-mat_other" }, { "text": "Electron guiding through insulating nanocapillaries: We simulate the electron transmission through insulating Mylar (PET)\ncapillaries. We show that the mechanisms underlying the recently discovered\nelectron guiding are fundamentally different from those for ion guiding.\nQuantum reflection and multiple near-forward scattering rather than the\nself-organized charge-up are key to the transmission along the capillary axis\nirrespective of the angle of incidence. We find surprisingly good agreement\nwith recent data. Our simulation suggests that electron guiding should also be\nobservable for metallic capillaries.", "category": "cond-mat_other" }, { "text": "Special relativity description of the heat propagation in Minkowski\n spacetime: In this paper we investigate the heat transport induced by continuous laser\nbeams up to an intensity of about 1029 Watt/cm2. We maintain that up to this\nintensity nonlinear effects are negligible and that the application of the\nlinear hyperbolic heat transport equation is fully justifiable. We show that\nthe Fourier diffusion equation gives the speed of diffusion, v > c and breaks\nthe causality of the thermal processes in Minkowski space-time. For hyperbolic\nheat transport v v_c$ where the transition finally occurs is related to the density $L_0$ of\nthe remanent vortices in the superfluid. Moreover, at temperatures below ca.\n0.5 K and in a small interval of velocity amplitudes between $v_c$ and a\nvelocity that is about 2% larger, the flow pattern is found to be unstable,\nswitching intermittently between potential flow and turbulence. From time\nseries recorded at constant temperature and driving force the distribution of\nthe excess velocities $\\Delta v = v_c^* - v_c$ is obtained and from that the\nfailure rate. Below 0.1 K we also can determine the distribution of the\nlifetimes of the phases of potential flow. Finally, the frequency dependence of\nthese results is discussed.", "category": "cond-mat_other" }, { "text": "Quantum liquid of repulsively bound pairs of particles in a lattice: Repulsively interacting particles in a periodic potential can form bound\ncomposite objects, whose dissociation is suppressed by a band gap. Nearly pure\nsamples of such repulsively bound pairs of cold atoms -- \"dimers\" -- have\nrecently been prepared by Winkler et al. [Nature 441, 853 (2006)]. We here\nderive an effective Hamiltonian for a lattice loaded with dimers only and\ndiscuss its implications to the many-body dynamics of the system. We find that\nthe dimer-dimer interaction includes strong on-site repulsion and\nnearest-neighbor attraction which always dominates over the dimer kinetic\nenergy at low temperatures. The dimers then form incompressible,\nminimal-surface \"droplets\" of a quantum lattice liquid. For low lattice\nfilling, the effective Hamiltonian can be mapped onto the spin-1/2 XXZ model\nwith fixed total magnetization which exhibits a first-order phase transition\nfrom the \"droplet\" to a \"gas\" phase. This opens the door to studying first\norder phase transitions using highly controllable ultracold atoms.", "category": "cond-mat_other" }, { "text": "Coherent adiabatic theory of two-electron quantum dot molecules in\n external spin baths: We derive an accurate molecular orbital based expression for the coherent\ntime evolution of a two-electron wave function in a quantum dot molecule where\nthe electrons interact with each other, with external time dependent\nelectromagnetic fields and with a surrounding nuclear spin reservoir. The\ntheory allows for direct numerical modeling of the decoherence in quantum dots\ndue to hyperfine interactions. Calculations result in good agreement with\nrecent singlet-triplet dephasing experiments by Laird et. al. [Phys. Rev. Lett.\n97, 056801 (2006)], as well as analytical model calculations. Furthermore, it\nis shown that using a much faster electric switch than applied in these\nexperiments will transfer the initial state to excited states where the\nhyperfine singlet-triplet mixing is negligible.", "category": "cond-mat_other" }, { "text": "The density maximum of He4 at the lambda point modeled by the stochastic\n quantum hydrodynamic analogy: The lambda point in liquid He4 is a well established phenomenon acknowledged\nas an example of Bose-Einstain condensation. This is generally accepted, but\nthere are serious discrepancies between the theory and experimental results,\nnamely the lower value of the transition temperature Tl and the negative value\nof dTl /dP. These discrepancies can be explained in term of the quantum\nstochastic hydrodynamic analogy (QSHA). The QSHA shows that at the\nHe4I\\textregisteredHe4II superfluid transition the quantum coherence length lc\nbecomes of order of the distance up to which the wave function of a couple of\nHe4 atoms extends itself. In this case, the He42 state is quantum and the\nquantum pseudo-potential brings a repulsive interaction that leads to the\nnegative dTl /dP behavior. This fact overcomes the difficulty to explain the\nphenomenon by introducing a Hamiltonian inter-atomic repulsive potential that\nwould obstacle the gas-liquid transition.", "category": "cond-mat_other" }, { "text": "Pseudospin excitations in coaxial nanotubes: In a 2DEG confined to two coaxial tubes the `tube degree of freedom' can be\ndescribed in terms of pseudospin-1/2 dynamics. The presence of tunneling\nbetween the two tubes leads to a collective oscillation known as pseudospin\nresonance. We employ perturbation theory to examine the dependence of the\nfrequency of this mode with respect to a coaxial magnetic field for the case of\nsmall intertube distances. Coulomb interaction leads to a shift of the\nresonance frequency and to a finite lifetime of the pseudospin excitations. The\npresence of the coaxial magnetic field gives rise to pronounced peaks in the\nshift of the resonance frequency. For large magnetic fields this shift vanishes\ndue to the effects of Zeeman splitting. Finally, an expression for the\nlinewidth of the resonance is derived. Numerical analysis of this expression\nsuggests that the linewidth strongly depends on the coaxial magnetic field,\nwhich leads to several peaks of the linewidth as well as regions where damping\nis almost completely suppressed.", "category": "cond-mat_other" }, { "text": "Superfluid hydrodynamics in fractal dimension space: The complex behavior of liquid ${}^4$He and liquid ${}^3$He in nanoporous\nmedia is determined by influence of randomly distributed geometrical\nconfinement as well as by significant contribution from the atoms near walls.\nIn the present paper fractional Schrodinger equation has been used for deriving\ntwo-fluid hydrodynamical equations for describing the motion of superfluid\nhelium in the fractal dimension space. Nonlinear equations for oscillations of\npressure and temperature are obtained and coupling of pressure and temperature\noscillations is observed. Moreover coupling should disappear at very low\ntemperatures which provide an experimental test for this theory.", "category": "cond-mat_other" }, { "text": "The scaling of the density of states in systems with resonance states: Resonance states of a two-electron quantum dot are studied using a\nvariational expansion with both real basis-set functions and complex scaling\nmethods. We present numerical evidence about the critical behavior of the\ndensity of states in the region where there are resonances. The critical\nbehavior is signaled by a strong dependence of some features of the density of\nstates with the basis-set size used to calculate it. The resonance energy and\nlifetime are obtained using the scaling properties of the density of states", "category": "cond-mat_other" }, { "text": "Luttinger parameter of quasi-one-dimensional para-H2: We have studied the ground-state properties of para-hydrogen in one dimension\nand in quasi-one-dimensional configurations using the path integral ground\nstate Monte Carlo method. This method produces zero-temperature exact results\nfor a given interaction and geometry. The quasi-one-dimensional setup has been\nimplemented in two forms: the inner channel inside a carbon nanotube coated\nwith H$_2$ and a harmonic confinement of variable strength. Our main result is\nthe dependence of the Luttinger parameter on the density within the stable\nregime. Going from one dimension to quasi-one dimension, keeping the linear\ndensity constant, produces a systematic increase of the Luttinger parameter.\nThis increase is however not enough to reach the superfluid regime and the\nsystem always remain in the quasi-crystal regime, according to Luttinger liquid\ntheory.", "category": "cond-mat_other" }, { "text": "On the Laser Stimulation of Low-Energy Nuclear Reactions in Deuterated\n Palladium: Models to account for the observed experimental results for low-energy\nnuclear reactions in palladium-deuteride systems are presented along with\ncalculated results. The crucial idea is a mechanism of improved probability for\nthe needed penetration of the Coulomb barrier for a D-D reaction. This\nfacilitation occurs, in general, with the formation of D^- ions at special\nfrequency modes (e.g. via phonons) and, specifically for the laser-stimulated\ncase, with utilization of enhanced optical potential at a selected interface.\nBoth mechanisms may work individually, or together, to increase the probability\nof barrier penetration.", "category": "cond-mat_other" }, { "text": "Coherent optical control of spin-spin interaction in doped\n semiconductors: We provide a theory of laser-induced interaction between spins localized by\nimpurity centers in a semiconductor host. By solving exactly the problem of two\nlocalized spins interacting with one itinerant exciton, an analytical\nexpression for the induced spin-spin interaction is given as a function of the\nspin separation, laser energy, and intensity. We apply the theory to shallow\nneutral donors (Si) and deep rare-earth magnetic impurities (Yb) in III-V\nsemiconductors. When the photon energy approaches a resonance related to\nexcitons bound to the impurities, the coupling between the localized spins\nincreases, and may change from ferromagnetic to anti-ferromagnetic. This\nlight-controlled spin interaction provides a mechanism for the quantum control\nof spins in semiconductors for quantum information processing; it suggests the\nrealization of spin systems whose magnetic properties can be controlled by\nchanging the strength and the sign of the spin-spin interaction.", "category": "cond-mat_other" }, { "text": "Detection of vortex coherent structures in superfluid turbulence: Filamentary regions of high vorticity irregularly form and disappear in the\nturbulent flows of classical fluids. We report an experimental comparative\nstudy of these so-called \" coherent structures \" in a classical versus quantum\nfluid, using liquid helium with a superfluid fraction varied from 0% up to 83%.\nThe low pressure core of the vorticity filaments is detected by pressure probes\nlocated on the sidewall of a 78-cm-diameter Von K\\'arm\\'an cell driven up to\nrecord turbulent intensity (R $\\lambda$ $\\sim$ $\\sqrt$ Re 10000). The\nstatistics of occurrence, magnitude and relative distribution of the filaments\nin a classical fluid are found indistinguishable from their superfluid\ncounterpart, namely the bundles of quantized vortex lines. This suggest that\nthe internal structure of vortex filaments, as well as their dissipative\nproperties have a negligible impact on their macroscopic dynamics, such as\nlifetime and intermittent properties.", "category": "cond-mat_other" }, { "text": "Correlation functions of cold bosons in an optical lattice: We investigate the experiment of collapses and revivals of matter wave field\nin more detail. To this end we calculate the lowest-order correlation functions\nof the Bose field. We compare predictions of the total Fock state with the\ncommonly used coherent state approximation. We also show how to observe an\ninterference pattern for the celebrated Mott state.", "category": "cond-mat_other" }, { "text": "Li Doping Effect on Properties and Phase Transfomations of Knbo3: Dielectric permittivity and infrared reflectivity spectra of Li doped KNbO3\nsingle crystals have been studied for the first time for K1-xLixNbO3 (KLN) with\nx = 0.015, 0.02, 0.065. It was found that like in KTaO3, Li admixture results\nin appearance of dielectric relaxation with the relaxation parameters very\nclose to those in KTaO3 quantum paraelectric. It was attributed to 90-grad\ndipole reorientation of Li+ <100> off centers substituted K+, which appear to\nbe presents as in paraelectric cubic phase as in ferroelectric phase down to\nlow temperatures. Besides, Li doping is accompanied by increasing of the\ncubic-tetragonal phase transition point, decreasing of\ntetragonal-orthorhombic-rhombohedral phase transition points and TO soft mode\nstiffen at room temperature.", "category": "cond-mat_other" }, { "text": "Vortices in Bose-Einstein Condensates: Some Recent Developments: In this brief review we summarize a number of recent developments in the\nstudy of vortices in Bose-Einstein condensates, a topic of considerable\ntheoretical and experimental interest in the past few years. We examine the\ngeneration of vortices by means of phase imprinting, as well as via dynamical\ninstabilities. Their stability is subsequently examined in the presence of\npurely magnetic trapping, and in the combined presence of magnetic and optical\ntrapping. We then study pairs of vortices and their interactions, illustrating\na reduced description in terms of ordinary differential equations for the\nvortex centers. In the realm of two vortices we also consider the existence of\nstable dipole clusters for two-component condensates. Last but not least, we\ndiscuss mesoscopic patterns formed by vortices, the so-called vortex lattices\nand analyze some of their intriguing dynamical features. A number of\ninteresting future directions are highlighted.", "category": "cond-mat_other" }, { "text": "Photon recycling in Fabry-Perot micro-cavities based on Si$_3$N$_4$\n waveguides: We present a numerical analysis and preliminary experimental results on\none-dimensional Fabry-Perot micro-cavities in Si$_3$N$_4$ waveguides. The\nFabry-Perot micro-cavities are formed by two distributed Bragg reflectors\nseparated by a straight portion of waveguide. The Bragg reflectors are composed\nby a few air slits produced within the Si$_3$N$_4$ waveguides. In order to\nincrease the quality factor of the micro-cavities, we have minimized, with a\nmultiparametric optimization tool, the insertion loss of the reflectors by\nvarying the length of their first periods (those facing the cavity). To explain\nthe simulation results the coupling of the fundamental waveguide mode with\nradiative modes in the Fabry-Perot micro-cavities is needed. This effect is\ndescribed as a recycling of radiative modes in the waveguide. To support the\nmodelling, preliminary experimental results of micro-cavities in Si$_3$N$_4$\nwaveguides realized with Focused Ion Beam technique are reported.", "category": "cond-mat_other" }, { "text": "Theoretical Studies on the Scanning Tunneling Microscope: The thesis explores calculating tunneling current densities between planar\nconducting electrodes in an STM. It considers factors like bias voltages and\nthe separation between electrodes, using Fermi energy and work functions. Pauli\nblocking effects on forward and reverse current densities are introduced,\ncomparing Airy function solutions with WKB results. A 'Russell Potential' is\ndefined for field lines, considering non-linearities and image force effects. A\nmulti-slice method using the transfer matrix approach calculates tunneling\ncurrents for the Russell Potential and trapezoid + image force potentials. The\nSimmons image potential's unreasonable enhancement of tunneling currents\nprompts the construction of models with distributed charge, which show\nnegligible image effects compared to trapezoidal potentials. Tunneling currents\nincrease with bias voltage, decrease exponentially with tip-sample distance,\nand rise with increasing tip curvature radius. The resolving power of the STM\ndegrades with blunter tips, higher bias voltages, and increased tip-sample\ndistances. In essence, the thesis covers calculating tunneling current\ndensities in STM, exploring different potential models and their effects. It\ndiscusses factors influencing tunneling behavior, like bias voltage, tip-sample\ndistance, and tip curvature, revealing limitations in imaging capabilities\nunder certain conditions.", "category": "cond-mat_other" }, { "text": "Large scale numerical simulations of \"ultrametric\" long-range depinning: The depinning of an elastic line interacting with a quenched disorder is\nstudied for long range interactions, applicable to crack propagation or\nwetting. An ultrametric distance is introduced instead of the Euclidean\ndistance, allowing for a drastic reduction of the numerical complexity of the\nproblem. Based on large scale simulations, two to three orders of magnitude\nlarger than previously considered, we obtain a very precise determination of\ncritical exponents which are shown to be indistinguishable from their Euclidean\nmetric counterparts. Moreover the scaling functions are shown to be unchanged.\nThe choice of an ultrametric distance thus does not affect the universality\nclass of the depinning transition and opens the way to an analytic real space\nrenormalization group approach.", "category": "cond-mat_other" }, { "text": "Semiclassical and quantum polarons in crystaline acetanilide: Crystalline acetanilide is a an organic solid with peptide bond structure\nsimilar to that of proteins. Two states appear in the amide I spectral region\nhaving drastically different properties: one is strongly temperature dependent\nand disappears at high temperatures while the other is stable at all\ntemperatures. Experimental and theoretical work over the past twenty five years\nhas assigned the former to a selftrapped state while the latter to an extended\nfree exciton state. In this article we review the experimental and theoretical\ndevelopments on acetanilide paying particular attention to issues that are\nstill pending. Although the interpretation of the states is experimentally\nsound, we find that specific theoretical comprehension is still lacking. Among\nthe issues that that appear not well understood is the effective dimensionality\nof the selftrapped polaron and free exciton states.", "category": "cond-mat_other" }, { "text": "Bose-Einstein condensates of polar molecules: anisotropic interactions =\n anisotropic mass: So far the theory of Bose-Einstein condensates (BEC) of polar molecules was\nbased on an ad hoc generalization of equations for spherical atoms. Here I\nadopt a rigorous pseudo-potential approach to low-energy dipolar interactions\nand derive a non-linear mean-field Schrodinger equation for a\nharmonically-trapped condensate. I show that, effectively, the dipolar\ninteractions alter molecular mass. The resulting effective mass is anisotropic:\nto the leading order the mass is altered only for the motion along the\npolarizing field. For a typical BEC of spin-polarized magnetically-interacting\nalkali-metal atoms the effective atomic mass is reduced by 10% from its bare\nvalue. For a BEC of polar molecules the mass may be reduced by a factor of a\n1,000.", "category": "cond-mat_other" }, { "text": "Bright solitary waves of atomic Bose-Einstein condensates under rotation: We analyse the rotation of bright solitary waves formed of atomic\nBose-Einstein condensates with attractive atomic interactions. By employing a\nvariational technique and assuming an irrotational quadrupolar flow field, we\nmap out the variational solutions in the rotating frame. In particular, we show\nthat rotation has a considerable stabilising effect on the system,\nsignificantly raising the critical threshold for collapse of the bright\nsolitary waves.", "category": "cond-mat_other" }, { "text": "Reaction Enhanced Diffusion in Spherical Membranes: The reversible reactions like A+B <-> C in the many-component diffusive\nsystem affect the diffusive properties of the constituents. The effective\nconjugation of irreversible processes of different dimensionality takes place\ndue to the stationarity in the system and can lead to essential increase of the\nresulting diffusive fluxes. The exact equations for the spatial concentration\nprofiles of the components are difficult to treat analytically. We solve\napproximately the equations for the concentration profiles of the\nreaction-diffusion components in the spherical geometry in the application to\nthe problem of the enhanced oxygen transfer through a biological membrane and\nto the mathematically similar problem of surface diffusion in a solid body. In\nthe latter case the spherical geometry can be an adequate tool for describing\nthe surface of a real solid body which can be modeled as a fractal object\nformed of sequences of spherical surfaces with different radii.", "category": "cond-mat_other" }, { "text": "Levels of self-consistency in the GW approximation: We perform $GW$ calculations on atoms and diatomic molecules at different\nlevels of self-consistency and investigate the effects of self-consistency on\ntotal energies, ionization potentials and on particle number conservation. We\nfurther propose a partially self-consistent $GW$ scheme in which we keep the\ncorrelation part of the self-energy fixed within the self-consistency cycle.\nThis approximation is compared to the fully self-consistent $GW$ results and to\nthe $G W_0$ and the $G_0W_0$ approximations. Total energies, ionization\npotentials and two-electron removal energies obtained with our partially\nself-consistent $GW$ approximation are in excellent agreement with fully\nself-consistent $GW$ results while requiring only a fraction of the\ncomputational effort. We also find that self-consistent and partially\nself-consistent schemes provide ionization energies of similar quality as the\n$G_0W_0$ values but yield better total energies and energy differences.", "category": "cond-mat_other" }, { "text": "Magnetization dynamics in dysprosium orthoferrites via inverse Faraday\n effect: The ultrafast non-thermal control of magnetization has recently become\nfeasible in canted antiferromagnets through photomagnetic instantaneous pulses\n[A.V. Kimel {\\it et al.}, Nature {\\bf 435}, 655 (2005)]. In this experiment\ncircularly polarized femtosecond laser pulses set up a strong magnetic field\nalong the wave vector of the radiation through the inverse Faraday effect,\nthereby exciting non-thermally the spin dynamics of dysprosium orthoferrites. A\ntheoretical study is performed by using a model for orthoferrites based on a\ngeneral form of free energy whose parameters are extracted from experimental\nmeasurements. The magnetization dynamics is described by solving coupled\nsublattice Landau-Lifshitz-Gilbert equations whose damping term is associated\nwith the scattering rate due to magnon-magnon interaction. Due to the inverse\nFaraday effect and the non-thermal excitation, the effect of the laser is\nsimulated by magnetic field Gaussian pulses with temporal width of the order of\nhundred femtoseconds. When the field is along the z-axis, a single resonance\nmode of the magnetization is excited. The amplitude of the magnetization and\nout-of-phase behavior of the oscillations for fields in z and -z directions are\nin good agreement with the cited experiment. The analysis of the effect of the\ntemperature shows that magnon-magnon scattering mechanism affects the decay of\nthe oscillations on the picosecond scale. Finally, when the field pulse is\nalong the x-axis, another mode is excited, as observed in experiments. In this\ncase the comparison between theoretical and experimental results shows some\ndiscrepancies whose origin is related to the role played by anisotropies in\northoferrites.", "category": "cond-mat_other" }, { "text": "Financial heat machine: We consider dynamics of financial markets as dynamics of expectations and\ndiscuss such a dynamics from the point of view of phenomenological\nthermodynamics. We describe a financial Carnot cycle and the financial analogue\nof a heat machine. We see, that while in physics a perpetuum mobile is\nabsolutely impossible, in economics such mobile may exist under some\nconditions. Our thermodynamical model for the financial market induces a rather\nunusual interpretation of the role of financial crises. In contrast to the\ncommon point of view, in our model financial crises play a crucial role in\nfunctioning of the modern financial market. This is an important (concluding)\nstage of any financial cycle that is analogous to the stage of cooling in the\nordinary Carnot cycle. A financial cycle could not be completed without such a\nstage as well as the ordinary Carnot cycle. Thus, in spite its destructive (at\nthe first sight) consequences the stage or financial crises is as well\nimportant as the stage of \"boiling of the financial market\" (\"heating of\nexpectations\")", "category": "cond-mat_other" }, { "text": "Ultrasensitive nanoelectromechanical mass detection: We describe the application of nanoelectromechanical systems (NEMS) to\nultrasensitive mass detection. In these experiments, a modulated flux of atoms\nwas adsorbed upon the surface of a 32.8 MHz NEMS resonator within an ultrahigh\nvacuum environment. The mass-induced resonance frequency shifts by these\nadsorbates were then measured to ascertain a mass sensitivity of 2.53x10^-18 g.\nIn these initial measurements, this sensitivity is limited by the noise in the\nNEMS displacement transducer; the ultimate, limits of the technique are set by\nfundamental phase noise processes. Our results and analysis indicate that mass\nsensing of individual molecules will be realizable with optimized NEMS devices.", "category": "cond-mat_other" }, { "text": "Topological Constraints on the Charge Distributions for the Thomson\n Problem: The method of Morse theory is used to analyze the distributions of unit\ncharges interacting through a repulsive force and constrained to move on the\nsurface of a sphere -- the Thomson problem. We find that, due to topological\nreasons, the system may organize itself in the form of pentagonal structures.\nThis gives a qualitative account for the interesting ``pentagonal buttons''\ndiscovered in recent numerical work.", "category": "cond-mat_other" }, { "text": "Comment on the paper \"Quasi-particle approach for lattice Hamiltonians\n with large coordination numbers\" by P. Navez, F. Queisser and R. Sch\u00fctzhold\n - J. Phys. A: Math. Theor. 47 225004 (2014): This comment regards a central aspect of the referred-to paper, the issue of\nconvergence of the large coordination-number expansion. Perturbation expansions\nof expressions containing a large number of parameters are generally invalid\ndue to the non-analyticity of the expanded expressions. I refer to recent work\nwhere these issues are analyzed and discussed in detail in relation to a\nbenchmark example of a cluster model. As discussed therein, methods which are\nuncontrollable and for which their convergence is not foreseeable are not only\nuseless but can mislead, particularly if models derived from them are used to\ninterpret experiments.", "category": "cond-mat_other" }, { "text": "A Guided Walk Down Wall Street: an Introduction to Econophysics: This article contains the lecture notes for the short course ``Introduction\nto Econophysics,'' delivered at the II Brazilian School on Statistical\nMechanics, held in Sao Carlos, Brazil, in February 2004. The main goal of the\npresent notes is twofold: i) to provide a brief introduction to the problem of\npricing financial derivatives in continuous time; and ii) to review some of the\nrelated problems to which physicists have made relevant contributions in recent\nyears.", "category": "cond-mat_other" }, { "text": "Observation of Majorana Quasiparticles Surface States in Superfluid\n ${^3}$He-B by Heat Capacity Measurements: We report about direct measurements of heat capacity of Majorana\nquasiparticles in superfluid ${^3}$He-B which appear near the surface of the\nexperimental bolometer on the coherence length ${\\xi}$. Two bolometers with\ndifferent surface-to-volume ratios were used which allows us to have different\ncalibrated contributions from Majorana quasiparticles to the ${^3}$He heat\ncapacity. Estimations of possible impact of ${^3}$He layers adsorbed on the\nwalls of the bolometer have been done.", "category": "cond-mat_other" }, { "text": "Stability of low-dimensional multicomponent Bose gases: I show that in low dimensions the interactions in dilute Bose mixtures are\nstrongly renormalized, which leads to a considerable change of stability\nconditions compared to the mean-field results valid in the high-density regime.\nEstimates are given for the two-component Bose-Hubbard model and for the\nRb(87)-K(41) mixture.", "category": "cond-mat_other" }, { "text": "Non-local density correlations as signal of Hawking radiation in BEC\n acoustic black holes: We have used the analogy between gravitational systems and non-homogeneous\nfluid flows to calculate the density-density correlation function of an atomic\nBose-Einstein condensate in the presence of an acoustic black hole. The\nemission of correlated pairs of phonons by Hawking-like process results into a\npeculiar long-range density correlation. Quantitative estimations of the effect\nare provided for realistic experimental configurations.", "category": "cond-mat_other" }, { "text": "Dynamic localization in an effective tight binding Hamiltonian model\n with a rapidly oscillating homogeneous electric field on a lattice: By the Magnus-Floquet approach we calculate the effective Hamiltonian for a\ncharged particle on the lattice subject to a homogeneous high frequency\noscillating electric field. The obtained result indicate the absence of dynamic\nlocalization of the particle for any value of the lattice constant and electric\nfield applied, which completes the limit results obtained by Dunlap and Kenkre.", "category": "cond-mat_other" }, { "text": "Critical Velocities for Roton and Super-Flow Quantum Turbulence in\n Liquid $^4$He: Two different types of transitions of the superfluid $^4$He to quantum\nturbulence regimes are studied for $1{\\rm D}$ geometry in the case when the\ninfluence of the normal fluid on superfluid flow is suppressed. It is shown\nthat the roton mechanism of transition to quantum turbulence leads to a\ncritical velocity satisfying the relation $v_c\\propto d^{-1/4}$. In the\nsuper-flow mechanism, the transition to quantum turbulence arises when the\n\"quantum Reynolds number\" is about $10^3$ and the critical velocity depends on\nchannel size $d$ as $v_c\\propto d^{-1}$ in agreement with the equations of\nmotion for a superfluid component of the liquid $^4$He being disturbed by small\nfluctuations of the normal fluid.", "category": "cond-mat_other" }, { "text": "Hard-core bosons on optical superlattices: Dynamics and relaxation in\n the superfluid and insulating regimes: We study the ground-state properties and nonequilibrium dynamics of hard-core\nbosons confined in one-dimensional lattices in the presence of an additional\nperiodic potential (superlattice) and a harmonic trap. The dynamics is analyzed\nafter a sudden switch-on or switch-off of the superlattice potential, which can\nbring the system into insulating or superfluid phases, respectively. A collapse\nand revival of the zero-momentum peak can be seen in the first case. We study\nin detail the relaxation of these integrable systems towards equilibrium. We\nshow how after relaxation time averages of physical observables, like the\nmomentum distribution function, can be predicted by means of a generalization\nof the Gibbs distribution.", "category": "cond-mat_other" }, { "text": "Modification to the pre-factor of the semiclassical propagator: We modify the pre-factor of the semiclassical propagator to improve its\nefficiency in practical implementations. The new pre-factor represents the\nsmooth portion of an orbit's contribution, and leads to fast convergence in\nnumerical calculations. As an illustration of the accuracy and efficiency of\nthe resultant propagator, we numerically calculate overlaps between quantum and\nsemiclassical wave functions, as well as low-lying spectrum density in a\n10-dimensional system contains unstable classical orbits. This sheds light on\napplying semiclassical propagator to high dimensional systems.", "category": "cond-mat_other" }, { "text": "Giant magnetic anisotropy of the bulk antiferromagnets IrMn and IrMn3: Theoretical predictions of the magnetic anisotropy of antiferromagnetic\nmaterials are demanding due to a lack of experimental techniques which are\ncapable of a direct measurement of this quantity. At the same time it is highly\nsignificant due to the use of antiferromagnetic components in magneto-resistive\nsensor devices where the stability of the antiferromagnet is of upmost\nrelevance. We perform an ab-initio study of the ordered phases of IrMn and\nIrMn3, the most widely used industrial antiferromagnets. Calculating the form\nand the strength of the magnetic anisotropy allows the construction of an\neffective spin model, which is tested against experimental measurements\nregarding the magnetic ground state and the Neel temperature. Our most\nimportant result is the extremely strong second order anisotropy for IrMn3\nappearing in its frustrated triangular magnetic ground state, a surprising fact\nsince the ordered L12 phase has a cubic symmetry. We explain this large\nanisotropy by the fact that cubic symmetry is locally broken for each of the\nthree Mn sub-lattices.", "category": "cond-mat_other" }, { "text": "Electronic structure via potential functional approximations: The universal functional of Hohenberg-Kohn is given as a coupling-constant\nintegral over the density as a functional of the potential. Conditions are\nderived under which potential-functional approximations are variational.\nConstruction via this method and imposition of these conditions are shown to\ngreatly improve the accuracy of the non-interacting kinetic energy needed for\norbital-free Kohn-Sham calculations.", "category": "cond-mat_other" }, { "text": "Experimental realization of BCS-BEC crossover physics with a Fermi gas\n of atoms: This thesis presents experiments probing physics in the crossover between\nBose-Einstein condensation (BEC) and BCS superconductivity using an ultracold\ngas of atomic fermions. Scattering resonances in these ultracold gases (known\nas Feshbach resonances) provide the unique ability to tune the fermion-fermion\ninteractions. The work presented here pioneered the use of fermionic Feshbach\nresonances as a highly controllable and tunable system ideal for studying the\ncusp of the BCS-BEC crossover problem. Here pairs of fermionic atoms have some\nproperties of diatomic molecules and some properties of Cooper pairs. I present\nstudies of a normal Fermi gas at a Feshbach resonance and the work required to\ncool the gas to temperatures where superfluidity in the crossover is predicted.\nThese studies culminated in our observation of a phase transition at the cusp\nof the BCS-BEC crossover through condensation of fermionic atom pairs. I also\ndiscuss subsequent work that confirmed the crossover nature of the pairs in\nthese condensates.", "category": "cond-mat_other" }, { "text": "Commensurability and hysteretic evolution of vortex configurations in\n rotating optical lattices: We present a theoretical study of vortices within a harmonically trapped\nBose-Einstein condensate in a rotating optical lattice. Due to the competition\nbetween vortex-vortex interactions and pinning to the optical lattice we find a\nvery complicated energy landscape, which leads to hysteretic evolution. The\nqualitative structure of the vortex configurations depends on the\ncommensurability between the vortex density and the site density -- with\nregular lattices when these are commensurate, and concentric rings when they\nare not. We model the imaging of these structures by calculating time-of-flight\ncolumn densities. As in the absence of the optical lattice, the vortices are\nmuch more easily observed in a time-of-flight image than \\emph{in-situ}.", "category": "cond-mat_other" }, { "text": "Diffusion and localization for the Chirikov typical map: We consider the classical and quantum properties of the \"Chirikov typical\nmap\", proposed by Boris Chirikov in 1969. This map is obtained from the well\nknown Chirikov standard map by introducing a finite number $T$ of random phase\nshift angles. These angles induce a random behavior for small time scales\n($tT$). We identify the classical chaos border $k_c\\sim T^{-3/2} \\ll 1$\nfor the kick parameter $k$ and two regimes with diffusive behavior on short and\nlong time scales. The quantum dynamics is characterized by the effect of\nChirikov localization (or dynamical localization). We find that the\nlocalization length depends in a subtle way on the two classical diffusion\nconstants in the two time-scale regime.", "category": "cond-mat_other" }, { "text": "Trapped Fermions across a Feshbach resonance with population imbalance: We investigate the phase separation of resonantly interacting fermions in a\ntrap with imbalanced spin populations, both at zero and at finite temperatures.\nWe directly minimize the thermodynamical potential under the local density\napproximation instead of using the gap equation, as the latter may give\nunstable solutions. On the BEC side of the resonance, one may cross three\ndifferent phases from the trap center to the edge; while on the BCS side or at\nresonance, typically only two phases show up. We compare our results with the\nrecent experiment, and the agreement is remarkable.", "category": "cond-mat_other" }, { "text": "On the free rotation of a molecule embedded in helium-4 clusters: The fact, that $^4$He atoms on different concentric circular paths around the\naxis of a quantum vortex move with identically equal angular momentum, which\nrepresents an important aspect of superfluidity of He-II, has been used to\ndiscover a model which can explain the {\\it typical nature} of experimentally\nobserved $N$ (number of $^4He$ atoms) dependence of the rotational constant\n($B$) of the rotor part of a cluster M:He$_N$. It reveals how exactly\nsuperfluidity is related to the said dependence of $B$ on $N$. We believe that\nthis model, when used with simulation techniques, would render results that\nwould agree closely with experiments.", "category": "cond-mat_other" }, { "text": "Laser Pulse Amplification with Bose-Einstein Condensates: This paper has been withdrawn by the author.", "category": "cond-mat_other" }, { "text": "Microstructure of He II in the presence of boundaries: We have studied the microstructure of a system of interacting Bose particles\nunder zero boundary conditions and have found two possible orderings. One\nordering is traditional and is characterized by the Bogolyubov dispersion law\nE^2 = (h^2 k^2/2m)^{2} + qn\\nu(k)[h^2 k^2/m] (with q=1) at a weak interaction.\nThe second one is new and is characterized by the same dispersion law, but with\nq=2^{-f}, where $f$ is the number of noncyclic coordinates. At a weak\ninteraction, the ground-state energy is less for the new solution. The\nboundaries affect the bulk microstructure due to the difference of the\ntopologies of closed and open systems.", "category": "cond-mat_other" }, { "text": "Momentum distribution of a freely expanding Lieb-Liniger gas: We numerically study free expansion of a few Lieb-Liniger bosons, which are\ninitially in the ground state of an infinitely deep hard-wall trap. Numerical\ncalculation is carried out by employing a standard Fourier transform, as\nfollows from the Fermi-Bose transformation for a time-dependent Lieb-Liniger\ngas. We study the evolution of the momentum distribution, the real-space\nsingle-particle density, and the occupancies of natural orbitals. Our numerical\ncalculation allows us to explore the behavior of these observables in the\ntransient regime of the expansion, where they are non-trivially affected by the\nparticle interactions. We derive analytically (by using the stationary phase\napproximation) the formula which connects the asymptotic shape of the momentum\ndistribution and the initial state. For sufficiently large times the momentum\ndistribution coincides (up to a simple scaling transformation) with the shape\nof the real-space single-particle density (the expansion is asymptotically\nballistic). Our analytical and numerical results are in good agreement.", "category": "cond-mat_other" }, { "text": "Empirical Formula of the Absolute Value of Electrical Conductivity for\n Elemental Metals and Its Interpretation By Fluctuation Dissipation Theorem: The absolute value of the electrical conductivity sigma of elemental metals\neven at the room temperature range is not well theoretically understood. This\nis particularly true in multivalent metals. This paper empirically found that\nsigma=n_{atom}e^2tau0/mG with tau0=hbar/k_{B}T reproduces the observations\nrather well for many metals as in Fig.1(b)-upper, if G is taken, by guessing to\nbe a summed number of electric bands counted from outer most orbitals. We find\nby comparative study at the same time n_{atom}=n, namely Z=1 and m=m^* for\nmajority of metals for sigma. Thus the only quantity remained is tau. The\nBardeen's tau is found equal to tau0 if the deformation potential is equal to\nFermi energy, using the observationally ascertained fact that thermal acoustic\nenergy=the Fermi energy. Since electrons behave nearly as free electrons, the\nwave function should show the minimum uncertainty relation of Delta p_{x}\nDelta_{x}=hbar/2, which following the classical Fluctuation-Dissipation-Theorem\nshows in fact tau0=hbar/k_{B}T.", "category": "cond-mat_other" }, { "text": "On Entropy Wind in Superfluid Helium: Generation of a quasi-stationary flow of the superfluid helium normal part in\nthe presence of intense first- and second-sound waves is studied. Relevant\nequations are obtained. The contribution to the process of energy dissipation\nat the shock front layer and of fluid viscosity is analysed in detail for the\ncase of a second-sound wave. An estimate concerning possible experimental\nobservation of the process is made.", "category": "cond-mat_other" }, { "text": "Magnetic vortex nucleation/annihilation in artificial-ferrimagnet\n microdisks: The topological nature of magnetic-vortex state gives rise to peculiar\nmagnetization reversal observed in magnetic microdisks. Interestingly,\nmagnetostatic and exchange energies which drive this reversal can be\neffectively controlled in artificial ferrimagnet heterostructures composed of\nrare-earth and transition metals. 25x[Py(t)/Gd(t)] (t=1 or 2 nm) superlattices\ndemonstrate a pronounced change of the magnetization and exchange stiffness in\na 10-300 K temperature range as well as very small magnetic anisotropy. Due to\nthese properties, the magnetization of cylindrical microdisks composed of these\nartificial ferrimagnets can be transformed from the vortex to\nuniformly-magnetized states in a permanent magnetic field by changing the\ntemperature. We explored the behavior of magnetization in 1.5-micrometer\n25x[Py(t)/Gd(t)] (t=1 or 2 nm) disks at different temperatures and magnetic\nfields and observed that due to the energy barrier separating vortex and\nuniformly-magnetized states, the vortex nucleation and annihilation occur at\ndifferent temperatures. This causes the temperature dependences of the Py/Gd\ndisks magnetization to demonstrate unique hysteretic behavior in a narrow\ntemperature range. It was discovered that for the 25x[Py(2 nm)/Gd(2 nm)]\nmicrodisks the vortex can be metastable at a certain temperature range.", "category": "cond-mat_other" }, { "text": "Experimental determination of the dipolar field in Mn12-acetate: Crystals of the molecular magnet Mn12-acetate are known to contain a small\nfraction of low- symmetry (minor) species with a small anisotropy barrier\nagainst spin reversal. The lower barrier leads to faster magnetic relaxation\nand lower coercive field. We exploit the low coercive fields of the minor\nspecies to make a direct determination of the dipole field in Mn12-ac. We find\nthat the dipolar field of a fully magnetized crystal is 51.5 \\pm 8.5 mT,\nconsistent with theoretical expectations.", "category": "cond-mat_other" }, { "text": "NMR in $^3$He-B: This text contains a collection of equations useful for understanding Nuclear\nMagnetic Resonance (NMR) experiments in superfluid $^3$He-B. This is a part of\nmy notebook where I try to describe some parts of this sophisticated system.", "category": "cond-mat_other" }, { "text": "Propagation of self-localised Q-ball solitons in the $^3$He universe: In relativistic quantum field theories, compact objects of interacting bosons\ncan become stable owing to conservation of an additive quantum number $Q$.\nDiscovering such $Q$-balls propagating in the Universe would confirm\nsupersymmetric extensions of the standard model and may shed light on the\nmysteries of dark matter, but no unambiguous experimental evidence exists. We\nreport observation of a propagating long-lived $Q$-ball in superfluid $^3$He,\nwhere the role of $Q$-ball is played by a Bose-Einstein condensate of magnon\nquasiparticles. We achieve accurate representation of the $Q$-ball Hamiltonian\nusing the influence of the number of magnons, corresponding to the charge $Q$,\non the orbital structure of the superfluid $^3$He order parameter. This\nrealisation supports multiple coexisting $Q$-balls which in future allows\nstudies of $Q$-ball dynamics, interactions, and collisions.", "category": "cond-mat_other" }, { "text": "Stroboscopic aliasing in long-range interacting quantum systems: We unveil a mechanism for generating oscillations with arbitrary multiplets\nof the period of a given external drive, in long-range interacting quantum\nmany-particle spin systems. These oscillations break discrete time translation\nsymmetry as in time crystals, but they are understood via two intertwined\nstroboscopic effects similar to the aliasing resulting from video taping a\nsingle fast rotating helicopter blade. The first effect is similar to a single\nblade appearing as multiple blades due to a frame rate that is in resonance\nwith the frequency of the helicopter blades' rotation; the second is akin to\nthe optical appearance of the helicopter blades moving in reverse direction.\nAnalogously to other dynamically stabilized states in interacting quantum\nmany-body systems, this stroboscopic aliasing is robust to detuning and\nexcursions from a chosen set of driving parameters, and it offers a novel route\nfor engineering dynamical $n$-tuplets in long-range quantum simulators, with\npotential applications to spin squeezing generation and entangled state\npreparation.", "category": "cond-mat_other" }, { "text": "Excitons in long molecular chains near the reflecting interface: We discuss coherent exciton-polariton states in long molecular chains that\nare formed due to the interaction of molecular excitations with both vacuum\nphotons and surface excitations of the neighboring reflecting substrate. The\nresonance coupling with surface plasmons (or surface polaritons) of the\nsubstrate can substantially contribute to the retarded intermolecular\ninteractions leading to an efficient channel of the decay of one-dimensional\nexcitons with small momenta via emission of surface excitations. The interface\nalso modifies the radiative decay of excitons into vacuum photons. In an\nidealized system, excitons with higher momenta would not emit photons nor\nsurface waves. For a dissipative substrate, additional exciton quenching takes\nplace owing to Joule losses as the electric field of the exciton polarization\npenetrates the substrate. We discuss how these effects depend on the\npolarization of molecular excitations, their frequency and on the distance of\nthe chain from the substrate.", "category": "cond-mat_other" }, { "text": "Electronic properties of ordered and disordered linear clusters of atoms\n and molecules: The electronic properties of one-dimensional clusters of N atoms or molecules\nhave been studied. The model used is similar to the Kronig-Penney model with\nthe potential offered by each ion being approximated by an attractive delta\nfunction. The energy eigenvalues, the eigenstates and the density of states are\ncalculated exactly for a linear cluster of N atoms or molecules. The dependence\nof these quantities on the various parameters of the problem show interesting\nbehavior. Effects of random distribution of the positions of the atoms and\nrandom distribution of the strengths of the potential have also been studied.\nThe results obtained in this paper can have direct applications for linear\nchain of atoms produced on metal surfaces or artificially created chain of\natoms by using scanning tunneling microscope or in studying molecular\nconduction of electrons across one-dimensional barriers.", "category": "cond-mat_other" }, { "text": "Thermodynamically consistent equilibrium properties of normal-liquid\n Helium-3: The high-precision data for the specific heat C_{V}(T,V) of normal-liquid\nHelium-3 obtained by Greywall, taken together with the molar volume V(T_0,P) at\none temperature T_0, are shown to contain the complete thermodynamic\ninformation about this phase in zero magnetic field. This enables us to\ncalculate the T and P dependence of all equilibrium properties of normal-liquid\nHelium-3 in a thermodynamically consistent way for a wide range of parameters.\nThe results for the entropy S(T,P), specific heat at constant pressure\nC_P(T,P), molar volume V(T,P), compressibility kappa(T,P), and thermal\nexpansion coefficient alpha(T,P) are collected in the form of figures and\ntables. This provides the first complete set of thermodynamically consistent\nvalues of the equilibrium quantities of normal-liquid Helium-3. We find, for\nexample, that alpha(T,P) has a surprisingly intricate pressure dependence at\nlow temperatures, and that the curves alpha(T,P) vs T do not cross at one\nsingle temperature for all pressures, in contrast to the curves presented in\nthe comprehensive survey of helium by Wilks.\n Corrected in cond-mat/9906222v3: The sign of the coefficient d_0 was\nmisprinted in Table I of cond-mat/9906222v1 and v2. It now correctly reads\nd_0=-7.1613436. All results in the paper were obtained with the correct value\nof d_0. (We would like to thank for E. Collin, H. Godfrin, and Y. Bunkov for\nfinding this misprint.)", "category": "cond-mat_other" }, { "text": "Three comments on the Fermi gas at unitarity in a harmonic trap: In this note we consider three issues related to the unitary Fermi gas in a\nharmonic trap. We present a short proof of a virial theorem, which states that\nthe average energy of a particle system at unitarity in a harmonic trap is\ntwice larger than the average potential energy. The theorem is valid for all\nsystems with no intrinsic scale, at zero or finite temperature. We discuss the\nodd-even splitting in a unitarity Fermi gas in a harmonic trap. We show that at\nlarge number of particles N the odd-even splitting is proportional to\nN^{1/9}\\hbar\\omega, with an undetermined numerical constant. We also show that\nfor odd N the lowest excitation energies are of order N^{-1/3}\\hbar\\omega.", "category": "cond-mat_other" }, { "text": "Measurements on Melting Pressure, Metastable Solid Phases, and Molar\n Volume of Univariant Saturated Helium Mixture: A concentration-saturated helium mixture at the melting pressure consists of\ntwo liquid phases and one or two solid phases. The equilibrium system is\nunivariant, whose properties depend uniquely on temperature. Four coexisting\nphases can exist on singular points, which are called quadruple points. As a\nunivariant system, the melting pressure could be used as a thermometric\nstandard. It would provide some advantages compared to the current reference,\nnamely pure $^3$He, especially at the lowest temperatures below 1 mK. We have\nextended the melting pressure measurements of the concentration-saturated\nhelium mixture from 10 mK to 460 mK. The density of the dilute liquid phase was\nalso recorded. The effect of the equilibrium crystal structure changing from\nhcp to bcc was clearly seen at T=294 mK at the melting pressure P=2.638 MPa. We\nobserved the existence of metastable solid phases around this point. No\nevidence was found for the presence of another, disputed, quadruple point at\naround 400 mK. The experimental results agree well with our previous\ncalculations at low temperatures, but deviate above 200 mK.", "category": "cond-mat_other" }, { "text": "Theory of Forces Induced by Evanescent Fields: We present the theoretical foundations of the interaction of electromagnetic\nevanescent fields on an object", "category": "cond-mat_other" }, { "text": "Anomalous Hall conductivity: local orbitals approach: A theory of the anomalous Hall conductivity based on the properties of single\nsite orbitals is presented. Effect of the finite electron life time is modeled\nby energy fluctuations of atomic-like orbitals. Transition from the ideal Bloch\nsystem for which the conductivity is determined by the Berry phase curvatures\nto the case of strong disorder for which the conductivity becomes dependent on\nthe relaxation time is analyzed. Presented tight-binding model gives by the\nunified way experimentally observed qualitative features of the anomalous\nconductivity in the so called good metal regime and that called as bad metal or\nhopping regime.", "category": "cond-mat_other" }, { "text": "Photon transport in a dissipative chain of nonlinear cavities: We analyze a chain of coupled nonlinear optical cavities driven by a coherent\nsource of light localized at one end and subject to uniform dissipation. We\ncharacterize photon transport by studying the populations and the photon\ncorrelations as a function of position. When complemented with input-output\ntheory, these quantities provide direct information about photon transmission\nthrough the system. The position of single- and multi-photon resonances\ndirectly reflect the structure of the many-body energy levels. This shows how a\nstudy of transport along a coupled cavity array can provide rich information\nabout the strongly correlated (many-body) states of light even in presence of\ndissipation. By means of a numerical algorithm based on the time-evolving block\ndecimation scheme adapted to mixed states, we are able to simulate arrays up to\nsixty cavities.", "category": "cond-mat_other" }, { "text": "The Effect Of Delay Times On The Optimal Velocity Traffic Flow Behavior: We have numerically investigated the effect of the delay times $\\tau_f$ and\n$\\tau_s$ of a mixture of fast and slow vehicles on the fundamental diagram of\nthe optimal velocity model. The optimal velocity function of the fast cars\ndepends not only on the headway of each car but also on the headway of the\nimmediately preceding one. It is found that the small delay times have almost\nno effects, while, for sufficiently large delay time $\\tau_s$ the current\nprofile displays qualitatively five different forms depending on $\\tau_f$,\n$\\tau_s$ and the fractions $d_f$ and $d_s$ of the fast and slow cars\nrespectively. The velocity (current) exhibits first order transitions at low\nand/or high densities, from freely moving phase to the congested state, and\nfrom congested state to the jamming one respectively accompanied by the\nexistence of a local minimal current. Furthermore, there exist a critical value\nof $\\tau_f$ above which the metastability and hysteresis appear. The\nspatial-temporal traffic patterns present more complex structure", "category": "cond-mat_other" }, { "text": "Generalized Mean Field Approach to a Resonant Bose-Fermi Mixture: We formulate a generalized mean-field theory of a mixture of fermionic and\nbosonic atoms, in which the fermion-boson interaction can be controlled by a\nFeshbach resonance. The theory correctly accounts for molecular binding\nenergies of the molecules in the two-body limit, in contrast to the most\nstraightforward mean-field theory. Using this theory, we discuss the\nequilibrium properties of fermionic molecules created from atom pairs in the\ngas. We also address the formation of molecules when the magnetic field is\nramped across the resonance, and present a simple Landau-Zener result for this\nprocess.", "category": "cond-mat_other" }, { "text": "Statics and dynamics of BEC's in double square well potentials: In this paper we treat the behavior of Bose Einstein condensates in double\nsquare well potentials, both of equal and different depths. For even depth,\nsymmetry preserving solutions to the relevant nonlinear Schr\\\"{o}dinger\nequation is known, just as in the linear limit. When the nonlinearity is strong\nenough, symmetry breaking solutions also exist, side by side with the symmetric\none. Interestingly, solutions almost entirely localized in one of the wells are\nknown as an extreme case. Here we outline a method for obtaining all these\nsolutions for repulsive interactions. The bifurcation point at which, for\ncritical nonlinearity, the asymmetric solutions branch off from the symmetry\npreserving ones is found analytically. We also find this bifurcation point and\ntreat the solutions generally via a Josephson Junction model.\n When the confining potential is in the form of two wells of different depth,\ninteresting new phenomena appear. This is true of both the occurrence of the\nbifurcation point for the static solutions, and also of the dynamics of phase\nand amplitude varying solutions. Again a generalization of the Josephson model\nproves useful. The stability of solutions is treated briefly.", "category": "cond-mat_other" }, { "text": "Dynamical instability and domain formation in a spin-1 Bose condensate: We interpret the recently observed spatial domain formation in spin-1 atomic\ncondensates as a result of dynamical instability. Within the mean field theory,\na homogeneous condensate is dynamically unstable (stable) for ferromagnetic\n(antiferromagnetic) atomic interactions. We find this dynamical instability\nnaturally leads to spontaneous domain formation as observed in several recent\nexperiments for condensates with rather small numbers of atoms. For trapped\ncondensates, our numerical simulations compare quantitatively to the\nexperimental results, thus largely confirming the physical insight from our\nanalysis of the homogeneous case.", "category": "cond-mat_other" }, { "text": "Classical and quantum dynamics of a model for atomic-molecular\n Bose--Einstein condensates: We study a model for a two-mode atomic-molecular Bose--Einstein condensate.\nStarting with a classical analysis we determine the phase space fixed points of\nthe system. It is found that bifurcations of the fixed points naturally\nseparate the coupling parameter space into four regions. The different regions\ngive rise to qualitatively different dynamics. We then show that this\nclassification holds true for the quantum dynamics.", "category": "cond-mat_other" }, { "text": "Modelling turbulent flow of superfluid $^4$He past a rough solid wall in\n the $T = 0$ limit: We present a numerical study, using the vortex filament model, of vortex\ntangles in a flow of pure superfluid $^4$He in the $T = 0$ limit through a\nchannel of width $D = 1$ mm for various applied velocities $V$. The flat\nchannel walls are assumed to be microscopically rough such that vortices\nterminating at the walls are permanently pinned; vortices are liberated from\ntheir pinned ends exclusively through self-reconnection with their images.\nSustained tangles were observed, for a period of 80 s, above the critical\nvelocity $V_c \\sim 0.20$ cm s$^{-1} = 20 \\kappa/D$. The coarse-grained velocity\nprofile was akin to a classical parabolic profile of the laminar Poiseuille\nflow, albeit with a non-zero slip velocity $\\sim$ 0.20 cm s$^{-1}$ at the\nwalls. The friction force was found to be proportional to the applied velocity.\nThe effective kinematic viscosity was $\\sim 0.1\\kappa$, and effective Reynolds\nnumbers within $\\mathrm{Re'} < 15$. The fraction of the polarized vortex length\nvaried between zero in the middle of the channel and $\\sim$ 60% within the\nshear flow regions $\\sim D/4$ from the walls. Therefore, we studied a state of\npolarized ultraquantum (Vinen) turbulence fuelled at short lengthscales by\nvortex reconnections, including those with vortex images due to the relative\nmotion between the vortex tangle and the pinning rough surface.", "category": "cond-mat_other" }, { "text": "Scanning optical homodyne detection of high-frequency picoscale\n resonances in cantilever and tuning fork sensors: Higher harmonic modes in nanoscale silicon cantilevers and microscale quartz\ntuning forks are detected and characterized using a custom scanning optical\nhomodyne interferometer. Capable of both mass and force sensing, these\nresonators exhibit high-frequency harmonic motion content with picometer-scale\namplitudes detected in a 2.5 MHz bandwidth, driven by ambient thermal\nradiation. Quartz tuning forks additionally display both in-plane and\nout-of-plane harmonics. The first six electronically detected resonances are\nmatched to optically detected and mapped fork eigenmodes. Mass sensing\nexperiments utilizing higher tuning fork modes indicate >6x sensitivity\nenhancement over fundamental mode operation.", "category": "cond-mat_other" }, { "text": "A model for luminescence of localized state ensemble: A distribution function for localized carriers,\n$f(E,T)=\\frac{1}{e^{(E-E_a)/k_BT}+\\tau_{tr}/\\tau_r}$, is proposed by solving a\nrate equation, in which, electrical carriers' generation, thermal escape,\nrecapture and radiative recombination are taken into account. Based on this\ndistribution function, a model is developed for luminescence from localized\nstate ensemble with a Gaussian-type density of states. The model reproduces\nquantitatively all the anomalous temperature behaviors of localized state\nluminescence. It reduces to the well-known band-tail and luminescence quenching\nmodels under certain approximations.", "category": "cond-mat_other" }, { "text": "The constitutive tensor of linear elasticity: its decompositions, Cauchy\n relations, null Lagrangians, and wave propagation: In linear anisotropic elasticity, the elastic properties of a medium are\ndescribed by the fourth rank elasticity tensor C. The decomposition of C into a\npartially symmetric tensor M and a partially antisymmetric tensors N is often\nused in the literature. An alternative, less well-known decomposition, into the\ncompletely symmetric part S of C plus the reminder A, turns out to be\nirreducible under the 3-dimensional general linear group. We show that the\nSA-decomposition is unique, irreducible, and preserves the symmetries of the\nelasticity tensor. The MN-decomposition fails to have these desirable\nproperties and is such inferior from a physical point of view. Various\napplications of the SA-decomposition are discussed: the Cauchy relations\n(vanishing of A), the non-existence of elastic null Lagrangians, the\ndecomposition of the elastic energy and of the acoustic wave propagation. The\nacoustic or Christoffel tensor is split in a Cauchy and a non-Cauchy part. The\nCauchy part governs the longitudinal wave propagation. We provide explicit\nexamples of the effectiveness of the SA-decomposition. A complete class of\nanisotropic media is proposed that allows pure polarizations in arbitrary\ndirections, similarly as in an isotropic medium.", "category": "cond-mat_other" }, { "text": "Transmodal Fabry-P\u00e9rot Resonance: Theory and Realization with Elastic\n Metamaterials: We discovered a new transmodal Fabry-P\\'erot resonance that one elastic-wave\nmode is maximally transmitted to another when the phase difference of two\ndissimilar modes through an anisotropic layer is exactly odd multiples of\n{\\pi}. Unlike the well-established Fabry-P\\'erot resonance, the transmodal\nresonance must involve two coupled elastic-wave modes, longitudinal and shear.\nThe formation of wiggly transmodal transmission spectra is due to structural\ninstability appearing in anisotropic mode-coupled elastic-media. Experiments\nwith elastic metamaterials confirmed our findings which can play a critical\nrole in shear-mode ultrasound applications.", "category": "cond-mat_other" }, { "text": "A priori Wannier functions from modified Hartree-Fock and Kohn-Sham\n equations: The Hartree-Fock equations are modified to directly yield Wannier functions\nfollowing a proposal of Shukla et al. [Chem. Phys. Lett. 262, 213-218 (1996)].\nThis approach circumvents the a posteriori application of the Wannier\ntransformation to Bloch functions. I give a novel and rigorous derivation of\nthe relevant equations by introducing an orthogonalizing potential to ensure\nthe orthogonality among the resulting functions. The properties of these,\nso-called a priori Wannier functions, are analyzed and the relation of the\nmodified Hartree-Fock equations to the conventional, Bloch-function-based\nequations is elucidated. It is pointed out that the modified equations offer a\ndifferent route to maximally localized Wannier functions. Their computational\nsolution is found to involve an effort that is comparable to the effort for the\nsolution of the conventional equations. Above all, I show how a priori Wannier\nfunctions can be obtained by a modification of the Kohn-Sham equations of\ndensity-functional theory.", "category": "cond-mat_other" }, { "text": "Threshold for Chaos and Thermalization in One-Dimensional Mean-Field\n Bose-Hubbard Model: We study the threshold for chaos and its relation to thermalization in the 1D\nmean-field Bose-Hubbard model, which in particular describes atoms in optical\nlattices. We identify the threshold for chaos, which is finite in the\nthermodynamic limit, and show that it is indeed a precursor of thermalization.\nFar above the threshold, the state of the system after relaxation is governed\nby the usual laws of statistical mechanics.", "category": "cond-mat_other" }, { "text": "Thermodynamic Measurements in a Strongly Interacting Fermi Gas: We conduct a series of measurements on the thermodynamic properties of an\noptically-trapped strongly interacting Fermi gas, including the energy $E$,\nentropy $S$, and sound velocity $c$. Our model-independent measurements of $E$\nand $S$ enable a precision study of the finite temperature thermodynamics. The\n$E(S)$ data are directly compared to several recent predictions. The\ntemperature in both the superfluid and normal fluid regime is obtained from the\nfundamental thermodynamic relation $T=\\partial E/\\partial S$ by parameterizing\nthe $E(S)$ data. Our $E(S)$ data are also used to experimentally calibrate the\nendpoint temperatures obtained for adiabatic sweeps of the magnetic field\nbetween the ideal and strongly interacting regimes. This enables the first\nexperimental calibration of the temperature scale used in experiments on\nfermionic pair condensation. Our calibration shows that the ideal gas\ntemperature measured for the onset of pair condensation corresponds closely to\nthe critical temperature estimated in the strongly interacting regime from the\nfits to our $E(S)$ data. The results are in very good agreement with recent\npredictions. Finally, using universal thermodynamic relations, we estimate the\nchemical potential and heat capacity of the trapped gas from the $E(S)$ data.", "category": "cond-mat_other" }, { "text": "Shear-strain-induced Spatially Varying Super-lattice Structures on\n Graphite studied by STM: We report on the Scanning Tunneling Microscope (STM) observation of linear\nfringes together with spatially varying super-lattice structures on (0001)\ngraphite (HOPG) surface. The structure, present in a region of a layer bounded\nby two straight carbon fibers, varies from a hexagonal lattice of 6nm\nperiodicity to nearly a square lattice of 13nm periodicity. It then changes\ninto a one-dimensional (1-D) fringe-like pattern before relaxing into a\npattern-free region. We attribute this surface structure to a shear strain\ngiving rise to a spatially varying rotation of the affected graphite layer\nrelative to the bulk substrate. We propose a simple method to understand these\nmoire patterns by looking at the fixed and rotated lattices in the Fourier\ntransformed k-space. Using this approach we can reproduce the spatially varying\n2-D lattice as well as the 1-D fringes by simulation. The 1-D fringes are found\nto result from a particular spatial dependence of the rotation angle.", "category": "cond-mat_other" }, { "text": "Highly sensitive and broadband carbon nanotube radio-frequency\n single-electron transistor: We have investigated radio-frequency single-electron transistor (RF-SET)\noperation of single-walled carbon nanotube quantum dots in the strong tunneling\nregime. At 4.2 K and carrier frequency 754.2 MHz, we reach a charge sensitivity\nof 2.3e-6 e/Hz^(1/2) over a bandwidth of 85 MHz. Our results indicate a\ngain-bandwidth product of 3.7e13 Hz^(3/2)/e, which is by one order of magnitude\nbetter than for typical RF-SETs.", "category": "cond-mat_other" }, { "text": "Counterflow quantum turbulence in a square channel under the normal\n fluid with a Poiseuille flow: We perform a numerical analysis of superfluid turbulence produced by thermal\ncounterflow in He II by using the vortex filament model. Counterflow in a low\naspect ratio channel is known to show the transition from laminar flow to the\ntwo turbulent states TI and TII. The present understanding is that the TI has\nthe turbulent superfluid and the laminar normal fluid but both fluids are\nturbulent in the TII state. This work studies the vortex tangle in the TI\nstate. Solid boundary condition is applied to walls of a square channel, and\nthe velocity field of the normal fluid is prescribed to be a laminar Poiseuille\nprofile. An inhomogeneous vortex tangle, which concentrates near the solid\nboundaries, is obtained as the statistically steady state. It is sustained by\nits characteristic space-time oscillation. The inhomogeneity of the vortex\ntangle shows the characteristic dependence on temperature, which is caused by\ntwo competitive effects, namely the profile of the counterflow velocity and the\nmutual friction.", "category": "cond-mat_other" }, { "text": "A new ripplon branch in He II: We analyse the dispersion relation of ripplons, on the surface of superfluid\nhelium, using the dispersive hydrodynamics approach and find a new ripplon\nbranch. We obtain analytical equation for the dispersion relation and analytic\nexpressions for the limiting cases. We discuss where ripplons can exist in the\nenergy-wavenumber plane. A numerical solution for the ripplon dispersion curve\nis obtained in the allowed regions. The new ripplon branch is found at energies\njust below the instability point.", "category": "cond-mat_other" }, { "text": "Strong magnetic coupling between an electronic spin qubit and a\n mechanical resonator: We describe a technique that enables a strong, coherent coupling between a\nsingle electronic spin qubit associated with a nitrogen-vacancy impurity in\ndiamond and the quantized motion of a magnetized nano-mechanical resonator tip.\nThis coupling is achieved via careful preparation of dressed spin states which\nare highly sensitive to the motion of the resonator but insensitive to\nperturbations from the nuclear spin bath. In combination with optical pumping\ntechniques, the coherent exchange between spin and motional excitations enables\nground state cooling and the controlled generation of arbitrary quantum\nsuperpositions of resonator states. Optical spin readout techniques provide a\ngeneral measurement toolbox for the resonator with quantum limited precision.", "category": "cond-mat_other" }, { "text": "The cold atom Hubbard toolbox: We review recent theoretical advances in cold atom physics concentrating on\nstrongly correlated cold atoms in optical lattices. We discuss recently\ndeveloped quantum optical tools for manipulating atoms and show how they can be\nused to realize a wide range of many body Hamiltonians. Then we describe\nconnections and differences to condensed matter physics and present\napplications in the fields of quantum computing and quantum simulations.\nFinally we explain how defects and atomic quantum dots can be introduced in a\ncontrolled way in optical lattice systems.", "category": "cond-mat_other" }, { "text": "Higher-order vortex solitons, multipoles, and supervortices on a square\n optical lattice: We predict new generic types of vorticity-carrying soliton complexes in a\nclass of physical systems including an attractive Bose-Einstein condensate in a\nsquare optical lattice (OL) and photonic lattices in photorefractive media. The\npatterns include ring-shaped higher-order vortex solitons and supervortices.\nStability diagrams for these patterns, based on direct simulations, are\npresented. The vortex ring solitons are stable if the phase difference \\Delta\n\\phi between adjacent solitons in the ring is larger than \\pi/2, while the\nsupervortices are stable in the opposite case, \\Delta \\phi <\\pi /2. A\nqualitative explanation to the stability is given.", "category": "cond-mat_other" }, { "text": "Bose-Einstein condensate in a quartic potential: Static and Dynamic\n properties: In this paper, we present a theoretical study of a Bose-Einstein condensate\nof interacting bosons in a quartic trap in one, two, and three dimensions.\nUsing Thomas-Fermi approximation, suitably complemented by numerical solutions\nof the Gross-Pitaevskii equation, we study the ground sate condensate density\nprofiles, the chemical potential, the effects of cross-terms in the quartic\npotential, temporal evolution of various energy components of the condensate,\nand width oscillations of the condensate. Results obtained are compared with\ncorresponding results for a bose condensate in a harmonic confinement.", "category": "cond-mat_other" }, { "text": "Optical Tamm states in one-dimensional magnetophotonic structures: We demonstrate the existence of a spectrally narrow localized surface state,\nthe so-called optical Tamm state, at the interface between a 1D magnetophotonic\nand non-magnetic photonic crystals. The state is spectrally located inside the\nphotonic band gaps of each of the photonic crystals comprising this\nmagnetophotonic structure. This state is associated with a sharp transmission\npeak through the sample and is responsible for the substantial enhancement of\nthe Faraday rotation for the corresponding wavelength. The experimental results\nare in excellent agreement with the theoretical predictions.", "category": "cond-mat_other" }, { "text": "Quasiparticle universes in Bose-Einstein condensates: Recent developments in simulating fundamental quantum field theoretical\neffects in the kinematical context of analogue gravity are reviewed.\nSpecifically, it is argued that a curved space-time generalization of the\nUnruh-Davies effect -- the Gibbons-Hawking effect in the de Sitter space-time\nof inflationary cosmological models -- can be implemented and verified in an\nultracold gas of bosonic atoms.", "category": "cond-mat_other" }, { "text": "Evaporative Cooling of a Photon Fluid to Quantum Degeneracy: We demonstrate that the process of evaporative cooling, as associated with\nthe cooling of atomic gases, can also be employed to condense a system of\nphotons giving rise to coherent properties of the light. The system we study\nconsists of photons in a high-quality Fabry-Perot cavity with photon\ninteractions mediated by a nonlinear atomic medium. We predict a macroscopic\noccupation of the lowest energy mode and evaluate the conditions for realizing\na narrow spectral width indicative of a long coherence time for the field.", "category": "cond-mat_other" }, { "text": "Entangling two defects via a surrounding crystal: We theoretically show how two impurity defects in a crystalline structure can\nbe entangled through coupling with the crystal. We demonstrate this with a\nharmonic chain of trapped ions in which two ions of a different species are\nembedded. Entanglement is found for sufficiently cold chains and for a certain\nclass of initial, separable states of the defects. It results from the\ninterplay between localized modes which involve the defects and the interposed\nions, it is independent of the chain size, and decays slowly with the distance\nbetween the impurities. These dynamics can be observed in systems exhibiting\nspatial order, viable realizations are optical lattices, optomechanical\nsystems, or cavity arrays in circuit QED.", "category": "cond-mat_other" }, { "text": "Quantum oscillations in a two-mode atom-molecule Bose-Einstein\n condensate -- the discrete WKB approach: Quantum effects in a system of coupled atomic and molecular Bose-Einstein\ncondensates in the framework of a two-mode model are studied numerically and\nanalytically, using the discrete WKB approach. In contrast to the mean-field\napproximation, the WKB analytical results are in a very good agreement with\nnumerical results. The quantum fluctuations of the atomic and molecular\npopulations are calculated, and found to be of the same order of magnitude as\ntheir mean values.", "category": "cond-mat_other" }, { "text": "Radial quadrupole and scissors modes in trapped Fermi gases across the\n BCS phase transition: The excitation spectra of the radial quadrupole and scissors modes of\nultracold Fermi gases in elongated traps are studied across the BCS\nsuperfluid-normal phase transition in the framework of a transport theory for\nquasiparticles. In the limit of zero temperature, this theory reproduces the\nresults of superfluid hydrodynamics, while in the opposite limit, above the\ncritical temperature, it reduces to the collisionless Vlasov equation. In the\nintermediate temperature range, the excitation spectra have two or three broad\npeaks, respectively, which are roughly situated at hydrodynamic and\ncollisionless frequencies, and whose strength is shifted from the hydrodynamic\nto the collisionless modes with increasing temperature. By fitting the time\ndependent quadrupole deformation with a damped oscillation of a single\nfrequency, we can understand the \"jump\" of the frequency of the radial\nquadrupole mode as a function of interaction strength which has recently been\nreported by the Innsbruck group.", "category": "cond-mat_other" }, { "text": "Hall Viscosity and the Acoustic Faraday Effect: For more than 20 years, observation of the non-dissipative Hall viscosity in\nthe quantum Hall effect has been impeded by the difficulty to probe directly\nthe momentum of the two-dimensional electron gas. However, in three-dimensional\nsystems such as superfluid ${}^{3}\\mathrm{He}\\!\\!-\\!\\!\\mathrm{B}$, the momentum\ndensity is readily probed through transverse acoustic waves. We show that in a\nthree-dimensional elastic medium supporting transverse waves, a non-vanishing\nHall viscosity induces circular birefringence. Such an effect has been observed\nin ${}^{3}\\mathrm{He}\\!\\!-\\!\\!\\mathrm{B}$ in the presence of a weak magnetic\nfield, and is known as the acoustic Faraday effect. The acoustic Faraday effect\nhas been understood in terms of the Zeeman splitting of the excited order\nparameter modes which support the transverse wave propagation in the\nsuperfluid. We show that the Zeeman effect can generically lead to a non-zero\nHall viscosity coefficient, and confirm this prediction using a simple\nphenomenological model for the ${}^{3}\\mathrm{He}\\!\\!-\\!\\!\\mathrm{B}$\ncollective modes. Therefore, we claim that the observation of the acoustic\nFaraday effect can be leveraged to make a direct observation of the Hall\nviscosity in superfluid ${}^{3}\\mathrm{He}\\!\\!-\\!\\!\\mathrm{B}$ in a magnetic\nfield and other systems such as the crystalline\n$\\mathrm{Tb}_{3}\\mathrm{Ga}_{5}\\mathrm{O}_{12}$ material.", "category": "cond-mat_other" }, { "text": "A simple model of Feshbach molecules: We present a two-channel model to describe the quantum state of two atoms\nwith finite-range interaction near a Feshbach resonance. This model provides a\nsimple picture to analytically derive the wave function and the binding energy\nof the molecular bound state. The results agree excellently with the\nmeasurements and multichannel calculations. For small binding energies, the\nsystem enters a threshold regime in which the Feshbach molecules are identical\nto long range atom pairs in single channel. According to their threshold\nbehavior, we find Feshbach resonances can be classified into two types.", "category": "cond-mat_other" }, { "text": "N-particle Bogoliubov vacuum state: We consider the Bogoliubov vacuum state in the number-conserving Bogoliubov\ntheory proposed by Castin and Dum [Phys. Rev. A 57, 3008 (1998)]. We show that\nin the particle representation the vacuum can be written in a simple diagonal\nform. The vacuum state can describe the stationary N-particle ground state of a\ncondensate in a trap, but it can also represent a dynamical state when, for\nexample, a Bose-Einstein condensate initially prepared in the stationary ground\nstate is subject to a time-dependent perturbation. In both cases the diagonal\nform of the Bogoliubov vacuum can be obtained by basically diagonalizing the\nreduced single particle density matrix of the vacuum. We compare N-body states\nobtained within the Bogoliubov theory with the exact ground states in a 3-site\nBose-Hubbard model. In this example, the Bogoliubov theory fails to accurately\ndescribe the stationary ground state in the limit when N goes to infinity but a\nsmall fraction of depleted particles is kept constant.", "category": "cond-mat_other" }, { "text": "A simple variational approach for an interacting Fermi trapped gas: Quantum states of a two-component Fermi trapped gas are described by\nintroducing an effective trap frequency, determined via variational techniques.\nClosed expressions for the contribution of a contact interaction potential to\nthe total energy and the pairing interaction are derived. They are valid for\nboth few and large number of particles, given the discrete nature of the\nformulation, and therefore richer than the continuous expressions, which are\nperfectly matched. Pairing energies within a shell are explicitly evaluated and\nits allowed values at a given energy level delimited. We show the importance of\nthe interaction over the trap energy as the number of particles ($N$) grows and\nthe temperature decreases. At zero temperature we find a polynomial dependence\nof the interaction energy on the Fermi energy, whose dominant term at large $N$\ncorresponds with the mean field approximation result. In addition, the role of\nthe strength of an attractive potential on the total energy is exhibited.", "category": "cond-mat_other" }, { "text": "Implications of experimental probes of the RG-flow in quantum Hall\n systems: We review the implications of the scaling data for the emergent symmetry of\nthe quantum Hall system. The location of the fixed points in the conductivity\nplane is consistent with the global, non-Abelian discrete symmetry $\\Gamma\n_{0}(2)$, and the renormalisation group (RG) flow-lines agree closely with that\nfound if the symmetry acts anti-holomorphically. We extend the analysis to\nconsider the rate of the RG flow. For a specific model in which the $\\Gamma\n_{0}(2)$ symmetry acts anti-holomorphically the scaling close to the fixed\npoints gives a critical delocalisation exponent $\\nu = 2.38\\pm 0.02$, in\nexcellent greement with direct measurements and with numerical simulations.\nBoth the predicted flow-lines and the flow rate also agree with the\nexperimental measurements far away from the critical points, suggesting an\nemergent topological structure capable of stabilising the symmetry predictions.\nWe hope that this agreement will stimulate further experimental study capable\nof conclusively testing the symmetry and exploring its associated dynamics.", "category": "cond-mat_other" }, { "text": "Entangling two defects via a surrounding crystal: We theoretically show how two impurity defects in a crystalline structure can\nbe entangled through coupling with the crystal. We demonstrate this with a\nharmonic chain of trapped ions in which two ions of a different species are\nembedded. Entanglement is found for sufficiently cold chains and for a certain\nclass of initial, separable states of the defects. It results from the\ninterplay between localized modes which involve the defects and the interposed\nions, it is independent of the chain size, and decays slowly with the distance\nbetween the impurities. These dynamics can be observed in systems exhibiting\nspatial order, viable realizations are optical lattices, optomechanical\nsystems, or cavity arrays in circuit QED.", "category": "cond-mat_other" }, { "text": "Sound velocities of hexagonal close-packed H2 and He under pressure: Bulk, shear, and compressional aggregate sound velocities of hydrogen and\nhelium in the close- packed hexagonal structure are calculated over a wide\npressure range using two complementary approaches: semi-empirical lattice\ndynamics based on the many-body intermolecular potentials and\ndensity-functional theory in the generalized gradient approximation. The sound\nvelocities are used to calculate pressure dependence of the Debye temperature.\nThe comparison between experiment and first-principle and semi-empirical\ncalculations provide constraints on the density dependence of intermolecular\ninteractions in the zero-temperature limit.", "category": "cond-mat_other" }, { "text": "Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He: We report measurements of the nuclear spin-lattice and spin-spin relaxation\ntimes of very dilute 3He in solid 4He in the temperature range 0.01 \\leq T \\leq\n0.5 K for densities where anomalies have been observed in torsional oscillator\nand shear modulus measurements. We compare the results with the values of the\nrelaxation times reported by other observers for higher concentrations and the\ntheory of Landesman that takes into account the elastic properties of the 4He\nlattice. A sharp increase in the magnitude of the nuclear spin-lattice\nrelaxation times compared to the the classical Landesman theory is observed\nclose to the temperatures where the torsional and shear modulus anomalies are\nobserved. The NMR results suggest that the tunneling of 3He impurities in the\natomic-scale elastic distortion is affected by the same processes that give\nrise to the macroscopic elastic dissipation anomalies.", "category": "cond-mat_other" }, { "text": "Ultrastrong coupling between a cavity resonator and the cyclotron\n transition of a 2D electron gas in the case of integer filling factor: We investigate theoretically the coupling between a cavity resonator and the\ncyclotron transition of a two dimensional electron gas under an applied\nperpendicular magnetic field. We derive and diagonalize an effective quantum\nHamiltonian describing the magnetopolariton excitations of the two dimensional\nelectron gas for the case of integer filling factors. The limits of validity of\nthe present approach are critically discussed. The dimensionless vacuum Rabi\nfrequency $\\Omega_0/\\omega_0$ (i.e., normalized to the cyclotron frequency\n$\\omega_0$) is shown to scale as $\\sqrt{\\alpha\\: n_{QW} \\nu}$, where $\\alpha$\nis the fine structure constant, $n_{QW}$ is the number of quantum wells and\n$\\nu$ is the filling factor in each well. We show that with realistic\nparameters of a high-mobility semiconductor two dimensional electron gas, the\ndimensionless coupling $\\Omega_0/\\omega_0$ can be much larger than 1 in the\ncase of $\\nu \\gg 1$, the latter condition being typically realized for\ncyclotron transitions in the microwave range. Implications of such ultrastrong\ncoupling regime are discussed.", "category": "cond-mat_other" }, { "text": "Dissipation-managed soliton in a quasi-one-dimensional Bose-Einstein\n condensate: We use the time-dependent mean-field Gross-Pitaevskii equation to study the\nformation of a dynamically-stabilized dissipation-managed bright soliton in a\nquasi-one-dimensional Bose-Einstein condensate (BEC). Because of three-body\nrecombination of bosonic atoms to molecules, atoms are lost (dissipated) from a\nBEC. Such dissipation leads to the decay of a BEC soliton. We demonstrate by a\nperturbation procedure that an alimentation of atoms from an external source to\nthe BEC may compensate for the dissipation loss and lead to a\ndynamically-stabilized soliton. The result of the analytical perturbation\nmethod is in excellent agreement with mean-field numerics. It seems possible to\nobtain such a dynamically-stabilized BEC soliton without dissipation in\nlaboratory.", "category": "cond-mat_other" }, { "text": "Influence of structure on the optical limiting properties of nanotubes: We investigate the role of carbon nanotubes structure on their optical\nlimiting properties. Samples of different and well-characterized structural\nfeatures are studied by optical limiting and pump-probe experiments. The\ninfluence of the diameter's size on the nano-object is demonstrated. Indeed,\nboth nucleation and growth of gas bubbles are expected to be sensitive to\ndiameter.", "category": "cond-mat_other" }, { "text": "The Boron Buckyball has an Unexpected Th Symmetry: The boron buckyball avoids the high symmetry icosahedral cage structure. The\npreviously reported Ih symmetric structure is not an energy minimum in the\npotential energy surface and exhibits a spontaneous symmetry breaking to yield\na puckered cage with a rare Th symmetry. The HOMO-LUMO gap is twice as large as\nthe reported value and amounts to 1.94 eV at B3LYP/6-31G(d) level. The valence\norbital structure of boron buckyball is identical to the one in the carbon\nanalogue.", "category": "cond-mat_other" }, { "text": "Proton transport and torque generation in rotary biomotors: We analyze the dynamics of rotary biomotors within a simple\nnano-electromechanical model, consisting of a stator part and a ring-shaped\nrotor having twelve proton-binding sites. This model is closely related to the\nmembrane-embedded F$_0$ motor of adenosine triphosphate (ATP) synthase, which\nconverts the energy of the transmembrane electrochemical gradient of protons\ninto mechanical motion of the rotor. It is shown that the Coulomb coupling\nbetween the negative charge of the empty rotor site and the positive stator\ncharge, located near the periplasmic proton-conducting channel (proton source),\nplays a dominant role in the torque-generating process. When approaching the\nsource outlet, the rotor site has a proton energy level higher than the energy\nlevel of the site, located near the cytoplasmic channel (proton drain). In the\nfirst stage of this torque-generating process, the energy of the\nelectrochemical potential is converted into potential energy of the\nproton-binding sites on the rotor. Afterwards, the tangential component of the\nCoulomb force produces a mechanical torque. We demonstrate that, at low\ntemperatures, the loaded motor works in the shuttling regime where the energy\nof the electrochemical potential is consumed without producing any\nunidirectional rotation. The motor switches to the torque-generating regime at\nhigh temperatures, when the Brownian ratchet mechanism turns on. In the\npresence of a significant external torque, created by ATP hydrolysis, the\nsystem operates as a proton pump, which translocates protons against the\ntransmembrane potential gradient. Here we focus on the F$_0$ motor, even though\nour analysis is applicable to the bacterial flagellar motor.", "category": "cond-mat_other" }, { "text": "Experimental realities refuting the existence of p=0 condensate in a\n system of interacting bosons : II. Spectroscopy of embedded molecules: Experimental observation of superfluidity in a microscopic cluster,\n$M:(^4He)_x$, of a molecule ($M$) and $x$ number of $^4He$ atoms (with $x$\nranging from 1 to many) is qualitatively analyzed. It concludes that: (i) each\n$^4He$ atom in the cluster has to have non-zero momentum for its confinement to\na space of size ($<$ the size of the cluster), (ii) superfluidity does not\nrequire atoms with zero momentum ($p=0$), and (iii) while all $^4He$ atoms in\nthe cluster cease to have relative motions (hence the inter-atomic collisions),\nthey retain a freedom to move coherently in order of their locations on a\nclosed path around the rotor ($M$ plus few nearest $^4He$ atoms which follow\nthe molecular rotation for their relatively strong binding with $M$). The\nanalysis also identifies the basic arrangement of $^4He$ atoms which allows the\nrotor to have free rotation in the cluster.", "category": "cond-mat_other" }, { "text": "The role of interactions in spin-polarised atomic Fermi gases at\n unitarity: We study the zero temperature properties of a trapped polarized Fermi gas at\nunitarity by assuming phase separation between an unpolarized superfluid and a\npolarized normal phase. The effects of the interaction are accounted using the\nformalism of quasi-particles to build up the equation of state of the normal\nphase with the Monte Carlo results for the relevant parameters. Our predictions\nfor the Chandrasekhar-Clogston limit of critical polarization and for the\ndensity profiles, including the density jump at the interface, are confirmed\nwith excellent accuracy by the recent experimental results at MIT. The role of\ninteraction on the radial width of the minority component, on the gap of the RF\ntransition and on the spin oscillations in the normal phase is also discussed.\nOur analysis points out the Fermi liquid nature of these strongly interacting\nspin polarized configurations.", "category": "cond-mat_other" }, { "text": "Hybrid apparatus for Bose-Einstein condensation and cavity quantum\n electrodynamics: Single atom detection in quantum degenerate gases: We present and characterize an experimental system in which we achieve the\nintegration of an ultrahigh finesse optical cavity with a Bose-Einstein\ncondensate (BEC). The conceptually novel design of the apparatus for the\nproduction of BECs features nested vacuum chambers and an in-vacuo magnetic\ntransport configuration. It grants large scale spatial access to the BEC for\nsamples and probes via a modular and exchangeable \"science platform\". We are\nable to produce \\87Rb condensates of five million atoms and to output couple\ncontinuous atom lasers. The cavity is mounted on the science platform on top of\na vibration isolation system. The optical cavity works in the strong coupling\nregime of cavity quantum electrodynamics and serves as a quantum optical\ndetector for single atoms. This system enables us to study atom optics on a\nsingle particle level and to further develop the field of quantum atom optics.\nWe describe the technological modules and the operation of the combined BEC\ncavity apparatus. Its performance is characterized by single atom detection\nmeasurements for thermal and quantum degenerate atomic beams. The atom laser\nprovides a fast and controllable supply of atoms coupling with the cavity mode\nand allows for an efficient study of atom field interactions in the strong\ncoupling regime. Moreover, the high detection efficiency for quantum degenerate\natoms distinguishes the cavity as a sensitive and weakly invasive probe for\ncold atomic clouds.", "category": "cond-mat_other" }, { "text": "Reduced Density Matrix Functional Theory at Finite Temperature:\n Theoretical Foundations: We present an ab-initio approach for grand canonical ensembles in thermal\nequilibrium with local or nonlocal external potentials based on the one-reduced\ndensity matrix. We show that equilibrium properties of a grand canonical\nensemble are determined uniquely by the eq-1RDM and establish a variational\nprinciple for the grand potential with respect to its one-reduced density\nmatrix. We further prove the existence of a Kohn-Sham system capable of\nreproducing the one-reduced density matrix of an interacting system at finite\ntemperature. Utilizing this Kohn-Sham system as an unperturbed system, we\ndeduce a many-body approach to iteratively construct approximations to the\ncorrelation contribution of the grand potential.", "category": "cond-mat_other" }, { "text": "Scaling issues for AlGaN/GaN HEMTs: performance optimization via devices\n geometry modelling: The potential barrier between source and gate in HEMTs and between source and\nchannel in MOSFET controls the current output and the velocity injection of\nelectrons in the channel [1], [2]. In non self aligned structures the electric\nfield behavior along the channel, for fixed applied voltages, is determined by\nthe contacts positions. Anyway, in GaAs based HEMTs, the geometry of the device\nappears to be not determinant for the output current due to saturation effects.\nOn the other hand, the GaN based technology still offers the possibility to\nenhance devices output current handling contacts distances. In this paper we\nwill present Monte Carlo simulations results which show how a downscaling of\nthe Source to Gate distance could improve the device performances inducing an\nhigher potential barrier between source and gate.", "category": "cond-mat_other" }, { "text": "Slow-wave effect and mode-profile matching in Photonic Crystal\n microcavities: Physical mechanisms involved in the light confinement in photonic crystal\nslab microcavities are investigated. We first present a full three-dimensional\nnumerical study of these microcavities. Then, to gain physical insight into the\nconfinement mechanisms, we develop a Fabry-Perot model. This model provides\naccurate predictions and sheds new light on the physics of light confinement.\nWe clearly identify two mechanisms to enhance the Q factor of these\nmicrocavities. The first one consists in improving the mode-profile matching at\nthe cavity terminations and the second one in using a slow wave in the cavity.", "category": "cond-mat_other" }, { "text": "Scale Separation Scheme for Simulating Superfluid Turbulence:\n Kelvin-Wave Cascade: A Kolmogorov-type cascade of Kelvin waves--the distortion waves on vortex\nlines--plays a key part in the relaxation of superfluid turbulence at low\ntemperatures. We propose an efficient numeric scheme for simulating the Kelvin\nwave cascade on a single vortex line. The idea is likely to be generalizable\nfor a full-scale simulation of different regimes of superfluid turbulence. With\nthe new scheme, we are able to unambiguously resolve the cascade spectrum\nexponent, and thus to settle the controversy between recent simulations [1] and\nrecently developed analytic theory [2].\n [1] W.F. Vinen, M. Tsubota and A. Mitani, Phys. Rev. Lett. 91, 135301 (2003).\n [2] E.V. Kozik and B.V. Svistunov, Phys. Rev. Lett. 92, 035301 (2004).", "category": "cond-mat_other" }, { "text": "Equations of Two-Fluid Hydrodynamics of Superfluid Helium with the\n Account of Electric Fields: System of two-fluid hydrodynamics of superfluid helium with the account of\nelectric field is obtained. These equations are obtained in kinetic approach\nusing quasi-equilibrium distribution function of quasi-particles, which vanishs\ncollision integral of quasi-particles, and contains dependence on electric\nfield by means of phenomenological parameter {\\alpha}. Using experimental data\nat temperature range of 1,4 - 2 K, where basic role plays roton hydrodynamics,\nthe value of phenomenological parameter, is obtained.", "category": "cond-mat_other" }, { "text": "Collective oscillations of a quasi one dimensional Bose condensate under\n damping: Influence of the damping on collective oscillations of a one-dimensional\ntrapped Bose gas in the mean field regime has been studied. Using the\nphenomenological damping approach developed by L.P. Pitaevskii, modified\nvariational equations for the parameters of the condensate wave function is\nderived. Analytical expressions for the condensate parameters in equilibrium\nstate have been obtained. Bistability in nonlinear oscillations of the\ncondensate under periodic variations of the trap potential is predicted. The\npredictions of the modified variational approach are confirmed by full\nnumerical simulations of the 1D GP equation with the damping.", "category": "cond-mat_other" }, { "text": "Comment to \"Mechanism for Designing Metamaterials with a High Index of\n Refraction\": Comment to \"Mechanism for Designing Metamaterials with a High Index of\nRefraction\" by J. T. Shen, Peter B. Catrysse and Shanhui Fan.", "category": "cond-mat_other" }, { "text": "Characterization of high-temperature PbTe p-n junctions prepared by\n thermal diffusion and by ion-implantation: We describe here the characteristics of two types of high-quality PbTe\np-n-junctions, prepared in this work: (1) by thermal diffusion of In4Te3 gas\n(TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and\nZn (Zn-IJ). The results, as presented here, demonstrate the high quality of\nthese PbTe diodes. Capacitance-voltage and current-voltage characteristics have\nbeen measured. The measurements were carried out over a temperature range from\n~ 10 K to ~ 180 K. The latter was the highest temperature, where the diode\nstill demonstrated rectifying properties. This maximum operating temperature is\nhigher than any of the earlier reported results.\n The saturation current density, J0, in both diode types, was ~ 10^-5 A/cm2 at\n80 K, while at 180 K J0 ~ 10^-1 A/cm2 in TDJ and ~ 1 A/cm2 in both\nion-implanted junctions. At 80 K the reverse current started to increase\nmarkedly at a bias of ~ 400 mV for TDJ, and at ~550 mV for IJ. The ideality\nfactor n was about 1.5-2 for both diode types at 80 K. The analysis of the C-V\nplots shows that the junctions in both diode types are linearly graded. The\nanalysis of the C-V plots allows also determining the height of the junction\nbarrier, the concentrations and the concentration gradient of the impurities,\nand the temperature dependence of the static dielectric constant. The\nzero-bias-resistance x area products (R0Ae) at 80 K are: 850 OHMcm2 for TDJ,\n250 OHMcm2 for In-IJ, and ~ 80 OHMcm2 for Zn-IJ, while at 180 K R0Ae ~ 0.38\nOHMcm2 for TDJ, and ~ 0.1 OHMcm2 for IJ. The estimated detectivity is: D* ~\n10^10 cmHz^(1/2)/W up to T=140 K, determined mainly by background radiation,\nwhile at T=180 K, D* decreases to 108-107 cmHz^(1/2)/W, and is determined by\nthe Johnson noise.", "category": "cond-mat_other" }, { "text": "Evidence for Efimov quantum states in an ultracold gas of cesium atoms: Systems of three interacting particles are notorious for their complex\nphysical behavior. A landmark theoretical result in few-body quantum physics is\nEfimov's prediction of a universal set of bound trimer states appearing for\nthree identical bosons with a resonant two-body interaction.\nCounterintuitively, these states even exist in the absence of a corresponding\ntwo-body bound state. Since the formulation of Efimov's problem in the context\nof nuclear physics 35 years ago, it has attracted great interest in many areas\nof physics. However, the observation of Efimov quantum states has remained an\nelusive goal. Here we report the observation of an Efimov resonance in an\nultracold gas of cesium atoms. The resonance occurs in the range of large\nnegative two-body scattering lengths, arising from the coupling of three free\natoms to an Efimov trimer. Experimentally, we observe its signature as a giant\nthree-body recombination loss when the strength of the two-body interaction is\nvaried. We also detect a minimum in the recombination loss for positive\nscattering lengths, indicating destructive interference of decay pathways. Our\nresults confirm central theoretical predictions of Efimov physics and represent\na starting point with which to explore the universal properties of resonantly\ninteracting few-body systems. While Feshbach resonances have provided the key\nto control quantum-mechanical interactions on the two-body level, Efimov\nresonances connect ultracold matter to the world of few-body quantum phenomena.", "category": "cond-mat_other" }, { "text": "Quantum Turbulence of Bellows-Driven 4He Superflow: Decay: We report on studies of quantum turbulence with second-sound in superfluid\n4He in which the turbulence is generated by the flow of the superfluid\ncomponent through a wide square channel, the ends of which are plugged with\nsintered silver superleaks, the flow being generated by compression of a\nbellows. The superleaks ensure that there is no net flow of the normal fluid.\nIn an earlier paper (Phys. Rev. B, 86, 134515 (2012)) we have shown that steady\nflow of this kind generates a density of vortex lines that is essentially\nidentical with that generated by thermal counterflow, when the average relative\nvelocity between the two fluids is the same. In this paper we report on studies\nof the temporal decay of the vortex-line density, observed when the bellows is\nstopped, and we compare the results with those obtained from the temporal decay\nof thermal counterflow re-measured in the same channel and under the same\nconditions. In both cases here is an initial fast decay which, for low enough\ninitial line density approaches for a short time the form $t^{-1}$\ncharacteristic of the decay of a random vortex tangle. This is followed at late\ntimes by a slower $t^{-3/2}$ decay, characteristic of the decay of large\n'quasi-classical eddies'. However, in the range of investigated parameters, we\nobserve always in the case of thermal counterflow, and only in a few cases of\nhigh steady-state velocity in superflow, an intermediate regime in which the\ndecay either does not proceed monotonically with time or passes through a point\nof inflexion. This difference, established firmly by our experiments, might\nrepresent one essential ingredient for the full theoretical understanding of\ncounterflow turbulence.", "category": "cond-mat_other" }, { "text": "New Heat-Capacity Measurements of the Possible Order-Disorder Transition\n in the 4/7-phase of 2D Helium: We have developed a new heat-capacity measuring system with ZYX graphite that\nis known to have much better crystallinity than Grafoil and started data\ncollection. We report preliminary data as well as a detailed description of\ninstrumentation including a mechanical heat-switch operated by hydraulic\npressure of superfluid helium-4.", "category": "cond-mat_other" }, { "text": "Non-perturbative embedding of local defects in crystalline materials: We present a new variational model for computing the electronic first-order\ndensity matrix of a crystalline material in presence of a local defect. A\nnatural way to obtain variational discretizations of this model is to expand\nthe difference Q between the density matrix of the defective crystal and the\ndensity matrix of the perfect crystal, in a basis of precomputed maximally\nlocalized Wannier functions of the reference perfect crystal. This approach can\nbe used within any semi-empirical or Density Functional Theory framework.", "category": "cond-mat_other" }, { "text": "Formation of a condensed state with macroscopic number of phonons in\n ultracold Bose gases: A mechanism for the formation of a new type of stationary state with\nmacroscopical number of phonons in condensed atomic gases is proposed. This\nmechanism is based on generating longitudinal phonons as a result of parametric\nresonance caused by a permanent modulation of the transverse trap frequency in\nan elongated trap. The phonon-phonon interaction predetermines the\nself-consistent evolution which is completed with macroscopic population of one\nfrom all levels within the energy interval of parametric amplification. This\nlevel proves to be shifted to the edge of this interval. All other levels end\nthe evolution with zero population.", "category": "cond-mat_other" }, { "text": "Exponentially Fragile PT-Symmetry in Lattices with Localized Eigenmodes: We study the effect of localized modes in lattices of size N with parity-time\n(PT) symmetry. Such modes are arranged in pairs of quasi-degenerate levels with\nsplitting delta exp{-N/xi}, where \\xi is their localization length. The level\n\"evolution\" with respect to the PT breaking parameter gamma shows a cascade of\nbifurcations during which a pair of real levels becomes complex. The\nspontaneous PT symmetry breaking occurs at gamma min(delta), thus resulting in\nan exponentially narrow exact PT phase. As N/xi decreases, it becomes more\nrobust with gamma (1/N)^2 and the distribution P(gamma) changes from log-normal\nto semi-Gaussian. Our theory can be tested in the frame of optical lattices.", "category": "cond-mat_other" }, { "text": "Three-body Recombination of Lithium-6 Atoms with Large Negative\n Scattering Lengths: The 3-body recombination rate at threshold for distinguishable atoms with\nlarge negative pair scattering lengths is calculated in the zero-range\napproximation. The only parameters in this limit are the 3 scattering lengths\nand the Efimov parameter, which can be complex valued. We provide semi-analytic\nexpressions for the cases of 2 or 3 equal scattering lengths and we obtain\nnumerical results for the general case of 3 different scattering lengths. Our\ngeneral result is applied to the three lowest hyperfine states of Lithium-6\natoms. Comparisons with recent experiments provide indications of loss features\nassociated with Efimov trimers near the 3-atom threshold.", "category": "cond-mat_other" }, { "text": "Spin dynamics of a trapped spin-1 Bose Gas above the Bose-Einstein\n transition temperature: We study collective spin oscillations in a spin-1 Bose gas above the\nBose-Einstein transition temperature. Starting from the Heisenberg equation of\nmotion, we derive a kinetic equation describing the dynamics of a thermal gas\nwith the spin-1 degree of freedom. Applying the moment method to the kinetic\nequation, we study spin-wave collective modes with dipole symmetry. The dipole\nmodes in the spin-1 system are found to be classified into the three type of\nmodes. The frequency and damping rate are obtained as functions of the peak\ndensity. The damping rate is characterized by three relaxation times associated\nwith collisions.", "category": "cond-mat_other" }, { "text": "Lindemann Criterion and the Anomalous Melting Curve of Sodium: Recent reports of the melting curve of sodium at high pressure have shown\nthat it has a very steep descent after a maximum of around 1000K at 31 GPa.\nThis is not due to a phase transition. According to the Lindemann criterion,\nthis behaviour should be apparent in the evolution of the Debye temperature\nwith pressure. In this work, we have performed an \"ab-initio\" analysis of the\nbehaviour of both the Debye temperature and the elastic constants up to 102\nGPa, and find a clear trend at high pressure that should cause a noticeable\neffect on the melting curve.", "category": "cond-mat_other" }, { "text": "Parametric spin excitations in lateral quantum dots: In this work, the spin dynamics of a single electron under parametric\nmodulation of a lateral quantum dot's electrostatic potential in the presence\nof spin-orbit coupling is investigated. Numerical and theoretical calculations\ndemonstrate that, by squeezing and/or moving the electron's wave function, spin\nrotations with Rabi frequencies on the order of tens of megahertz can be\nachieved with experimentally accessible parameters in both parabolic and square\nlateral quantum dots. Applications of parametric excitations for determining\nspin-orbit coupling parameters and for increasing the spin polarization in the\nelectronic ground are demonstrated.", "category": "cond-mat_other" }, { "text": "Exact Study of the 1D Boson Hubbard Model with a Superlattice Potential: We use Quantum Monte Carlo simulations and exact diagonalization to explore\nthe phase diagram of the Bose-Hubbard model with an additional superlattice\npotential. We first analyze the properties of superfluid and insulating phases\npresent in the hard-core limit where an exact analytic treatment is possible\nvia the Jordan-Wigner transformation. The extension to finite on-site\ninteraction is achieved by means of quantum Monte Carlo simulations. We\ndetermine insulator/superfluid phase diagrams as functions of the on-site\nrepulsive interaction, superlattice potential strength, and filling, finding\nthat insulators with fractional occupation numbers, which are present in the\nhard-core case, extend deep into the soft-core region. Furthermore, at integer\nfillings, we find that the competition between the on-site repulsion and the\nsuperlattice potential can produce a phase transition between a Mott insulator\nand a charge density wave insulator, with an intermediate superfluid phase. Our\nresults are relevant to the behavior of ultracold atoms in optical\nsuperlattices which are beginning to be studied experimentally.", "category": "cond-mat_other" }, { "text": "Experimental study of the transport of coherent interacting matter-waves\n in a 1D random potential induced by laser speckle: We present a detailed analysis of the 1D expansion of a coherent interacting\nmatterwave (a Bose-Einstein condensate) in the presence of disorder. A 1D\nrandom potential is created via laser speckle patterns. It is carefully\ncalibrated and the self-averaging properties of our experimental system are\ndiscussed. We observe the suppression of the transport of the BEC in the random\npotential. We discuss the scenario of disorder-induced trapping taking into\naccount the radial extension in our experimental 3D BEC and we compare our\nexperimental results with the theoretical predictions.", "category": "cond-mat_other" }, { "text": "Topological quantum correction to an atomic ideal gas law as a dark\n energy effect: The traditional ambiguity about the bulk electrostatic potentials in crystals\nis due to the conditional convergence of Coulomb series. The classical Ewald\napproach turns out to be the first one resolving this task as consistent with a\ntranslational symmetry. The latter result appears to be directly associated\nwith the thermodynamic limit in crystals. In this case the solution can also be\nobtained upon direct lattice summation, but after subtracting the mean Bethe\npotential. As shown, this effect is associated with special periodic boundary\nconditions at infinity so as to neutralize an arbitrary choice of the unit-cell\ncharge distribution. However, the fact that any additional potential exerted by\nsome charge distribution must in turn affect that charge distribution in\nequilibrium is not discussed in the case at hand so far. Here we show that in\nthe simplest event of gaseous atomic hydrogen as an example, the\nself-consistent mean-field-potential correction results in an additional\npressure contribution to an ideal gas law. As a result, the corresponding\ncorrection to the sound velocity arises. Moreover, if gas in question is not\nbounded by any fixed volume, then some acceleration within that medium is\nexpected. Addressed to the Friedman hypersphere, our result may be interesting\nin connection with the accelerating Universe revealed experimentally and\ndiscussed intensively.", "category": "cond-mat_other" }, { "text": "Vortex Properties of a Resonant Superfluid: The properties of a vortex in a rotating superfluid Fermi gas are studied in\nthe unitary limit. A phenomenological approach based on Ginzburg-Landau theory\nis developed for this purpose. The density profiles, including those of the\nnormal fluid and superfluid, are obtained at various temperatures and rotation\nfrequencies. The superfluid and normal fluid densities can be identified from\nthe angular momentum density. The total free energy and angular momentum of the\nvortex are also obtained.", "category": "cond-mat_other" }, { "text": "Dynamics of rapidly rotating Bose-Einstein condensates in a harmonic\n plus quartic trap: A two-dimensional rapidly rotating Bose-Einstein condensate in a harmonic\nplus quartic trap is expected to have unusual vortex states that do not occur\nin a pure harmonic trap. At a critical rotation speed $\\Omega_h$, a central\nhole appears in the condensate, and at some faster rotation speed $\\Omega_g$,\nthe system undergoes a transition to a giant vortex state with pure\nirrotational flow. Using a time-dependent variational analysis, we study the\nbehavior of an annular condensate with a single concentric ring of vortices.\nThe transition to a giant vortex state is investigated by comparing the energy\nof the two equilibrium states (the ring of vortices and the giant vortex) and\nalso by studying the dynamical stability of small excitation modes of the ring\nof vortices.", "category": "cond-mat_other" }, { "text": "Exactly solvable model of electron in the Lame potential and\n singularities of the electron thermodynamic potential: One-gap and two-gap separable Lame potentials are studied in detail. For the\none-dimensional case, we construct the dispersion relation graph E(k) and for\nthe three-dimensional case we construct the Fermi surfaces in the first and\nsecond bands. The pictures illustrate a passage from the limit case of free\nelectrons to the limit case of tight binding electrons. These results are used\nto describe the Lifshits electron phase transition of 2.5 kind and derive some\nexact expressions. We also examine the singularities of the second derivative\nof magnetic momentum in an external magnetic field. The parameter of the\nsingularities depends on corresponding effective mass.", "category": "cond-mat_other" }, { "text": "Half-vortices in polariton condensates: It is shown that vortices in linearly polarized polariton condensates in\nplanar semiconductor microcavities carry two winding numbers (k,m). These\nnumbers can be either integer or half-integer simultaneously. Four half-integer\nvortices (1/2,1/2), (-1/2,-1/2), (1/2,-1/2), and (-1/2,1/2) are anisotropic,\npossess the smallest energy, and define the Kosterlitz-Thouless transition\ntemperature. The condensate concentration remains finite within the core of\nhalf-vortex and the polarization becomes fully circular in the core center.", "category": "cond-mat_other" }, { "text": "Influence of an external magnetic field on the decoherence of a central\n spin coupled to an antiferromagnetic environment: Using the spin wave approximation, we study the decoherence dynamics of a\ncentral spin coupled to an antiferromagnetic environment under the application\nof an external global magnetic field. The external magnetic field affects the\ndecoherence process through its effect on the antiferromagnetic environment. It\nis shown explicitly that the decoherence factor which displays a Gaussian decay\nwith time depends on the strength of the external magnetic field and the\ncrystal anisotropy field in the antiferromagnetic environment. When the values\nof the external magnetic field is increased to the critical field point at\nwhich the spin-flop transition (a first-order quantum phase transition) happens\nin the antiferromagnetic environment, the decoherence of the central spin\nreaches its highest point. This result is consistent with several recent\nquantum phase transition witness studies. The influences of the environmental\ntemperature on the decoherence behavior of the central spin are also\ninvestigated.", "category": "cond-mat_other" }, { "text": "Vortex-line solitons in a periodically modulated Bose gas: We study the nonlinear excitations of a vortex-line in a Bose-Einstein\ncondensate trapped in a one-dimensional optical lattice. We find that the\nclassical Euler dynamics of the vortex results in a description of the vortex\nline in terms of a (discrete) one-dimensional Gross-Pitaevskii equation, which\nallows for both bright and gray soliton solutions. We discuss these solutions\nin detail and predict that it is possible to create vortex-line solitons with\ncurrent experimental capabilities.", "category": "cond-mat_other" }, { "text": "Neutron Reflection from the Surface of Liquid 4He with and without a\n Layer of 3He: We report and discuss the first neutron reflection measurements from the free\nsurface of normal and superfluid 4He and of liquid 3He-4He mixture. In case of\nliquid 4He the surface roughness is different above and below the lambda\ntransition, being smoother in the superfluid state. For the superfluid, we also\nobserve the formation of a surface layer ~200 A thick which has a subtly\ndifferent neutron scattering cross-section. The results can be interpreted as\nan enhancement of Bose-Einstein condensate fraction close to the helium\nsurface. We find that the addition of 3He isotopic impurities leads to the\nformation of Andreev levels at low temperatures.", "category": "cond-mat_other" }, { "text": "Spin Collective Modes of Two-Species Fermi Liquids: Helium-3 and Atomic\n Gases near the Feshbach Resonance: We present theoretical findings on the spin collective modes of a two-species\nFermi liquid, prepared alternatively in a polarized equilibrium or a polarized\nnon-equilibrium state. We explore the effects on these modes of a diverging\ns-wave scattering length, as occurs near a Feshbach resonance in a Fermionic\natomic gas. We compare these atomic gas modes with those of the conventional\nHelium-3 system, and we find that they differ from the conventional systems,\nand that the gap and spin stiffness are tunable via the Feshbach resonance.", "category": "cond-mat_other" }, { "text": "Statistical Facts of Artificial Stock Market: The paper reports the construction of artificial stock market that emerges\nthe similar statistical facts with real data in Indonesian stock market. We use\nthe individual but dominant data, i.e.: PT TELKOM in hourly interval. The\nartificial stock market shows standard statistical facts, e.g.: volatility\nclustering, the excess kurtosis of the distribution of return, and the scaling\nproperties with its breakdown in the crossover of Levy distribution to the\nGaussian one. From this point, the artificial stock market will always be\nevaluated in order to have comprehension about market process in Indonesian\nstock market generally.", "category": "cond-mat_other" }, { "text": "The role of the coherence in the cross-correlation analysis of\n diffraction patterns from two-dimensional dense mono-disperse systems: The investigation of the static and dynamic structural properties of\ncolloidal systems relies on techniques capable of atomic resolution in real\nspace and femtosecond resolution in time. Recently, the cross-correlation\nfunction (CCF) analysis of both X-rays and electron diffraction patterns from\ndilute and dense aggregates has demonstrated the ability to retrieve\ninformation on the sample's local order and symmetry. Open questions remain\nregarding the role of the beam coherence in the formation of the diffraction\npattern and the properties of the CCF, especially in dense systems. Here, we\nsimulate the diffraction patterns of dense two-dimensional monodisperse systems\nof different symmetries, varying the transverse coherence of the probing wave,\nand analyze their CCF. We study samples with different symmetries at different\nsize scale, as for example, pentamers arranged into a four-fold lattice where\neach pentamer is surrounded by triangular lattices, both ordered and\ndisordered. In such systems, different symmetry modulations are arising in the\nCCF at specific scattering vectors. We demonstrate that the amplitude of the\nCCF is a fingerprint of the degree of the ordering in the sample and that at\npartial transverse coherence, the CCF of a dense sample corresponds to that of\nan individual scattering object.", "category": "cond-mat_other" }, { "text": "Quantized vortices in atomic Bose-Einstein condensates: In this review, we give an overview of the experimental and theoretical\nadvances in the physics of quantized vortices in dilute atomic-gas\nBose--Einstein condensates in a trapping potential, especially focusing on\nexperimental research activities and their theoretical interpretations. Making\ngood use of the atom optical technique, the experiments have revealed many\nnovel structural and dynamic properties of quantized vortices by directly\nvisualizing vortex cores from an image of the density profiles. These results\nlead to a deep understanding of superfluid hydrodynamics of such systems.\nTypically, vortices are stabilized by a rotating potential created by a laser\nbeam, magnetic field, and thermal gas. Finite size effects and inhomogeneity of\nthe system, originating from the confinement by the trapping potential, yield\nunique vortex dynamics coupled with the collective excitations of the\ncondensate. Measuring the frequencies of the collective modes is an accurate\ntool for clarifying the character of the vortex state. The topics included in\nthis review are the mechanism of vortex formation, equilibrium properties, and\ndynamics of a single vortex and those of a vortex lattice in a rapidly rotating\ncondensate.", "category": "cond-mat_other" }, { "text": "Simulations of financial markets in a Potts-like model: A three-state model based on the Potts model is proposed to simulate\nfinancial markets. The three states are assigned to \"buy\", \"sell\" and\n\"inactive\" states. The model shows the main stylized facts observed in the\nfinancial market: fat-tailed distributions of returns and long time\ncorrelations in the absolute returns. At low inactivity rate, the model\neffectively reduces to the two-state model of Bornholdt and shows similar\nresults to the Bornholdt model. As the inactivity increases, we observe the\nexponential distributions of returns.", "category": "cond-mat_other" }, { "text": "Low-Temperature Mobility of Surface Electrons and Ripplon-Phonon\n Interaction in Liquid Helium: The low-temperature dc mobility of the two-dimensional electron system\nlocalized above the surface of superfluid helium is determined by the slowest\nstage of the longitudinal momentum transfer to the bulk liquid, namely, by the\ninteraction of surface and volume excitations of liquid helium, which rapidly\ndecreases with temperature. Thus, the temperature dependence of the\nlow-frequency mobility is \\mu_{dc} = 8.4x10^{-11}n_e T^{-20/3} cm^4 K^{20/3}/(V\ns), where n_e is the surface electron density. The relation\nT^{20/3}E_\\perp^{-3} << 2x10^{-7} between the pressing electric field (in\nkV/cm) and temperature (in K) and the value \\omega < 10^8 T^5 K^{-5}s^{-1} of\nthe driving-field frequency have been obtained, at which the above effect can\nbe observed. In particular, E_\\perp = 1 kV/cm corresponds to T < 70 mK and\n\\omega/2\\pi < 30 Hz.", "category": "cond-mat_other" }, { "text": "Binding Energies of 6Li p-wave Feshbach Molecules: We present measurements of the binding energies of $^6$Li p-wave Feshbach\nmolecules formed in combinations of the (F = 1/2, m_F = +1/2), (1), and (F =\n1/2, m_F = -1/2), (2), states. The binding energies scale linearly with\nmagnetic field detuning for all three resonances. The relative molecular\nmagnetic moments are found to be $113 \\pm 7 \\mu$K/G, $111 \\pm 6 \\mu$K/G and\n$118 \\pm 8 \\mu$K/G for the (1)-(1), (1)-(2) and (2)-(2) resonances,\nrespectively, in good agreement with theoretical predictions. Closed channel\namplitudes and the size of the p-wave molecules are obtained theoretically from\nfull closed-coupled calculations.", "category": "cond-mat_other" }, { "text": "Rotating states for trapped bosons in an optical lattice: Rotational states for trapped bosons in an optical lattice are studied in the\nframework of the Hubbard model. Critical frequencies are calculated and the\nmain parameter regimes are identified. Transitions are observed from edge\nsuperfluids to vortex lattices with Mott insulating cores, and subsequently to\nlattices of interstitial vortices. The former transition coincides with the\nMott transition. Changes in symmetry of the vortex lattices are observed as a\nfunction of lattice depth. Predictions for experimental signatures are\npresented.", "category": "cond-mat_other" }, { "text": "Two objective and independent fracture parameters for interface cracks\n and a paradox: Due to the oscillatory singular stress field around a crack tip, interface\nfracture has some peculiar features. This paper is focused on two of them. One\ncan be reflected by a proposed paradox that geometrically similar structures\nwith interface cracks under similar loadings may have different failure\nbehaviors. The other one is that the existing fracture parameters of the\noscillatory singular stress field, such as a complex stress intensity factor,\nexhibit some non-objectivity because their phase angle depend on an arbitrarily\nchosen length. Two objective and independent fracture parameters are proposed\nwhich can fully characterize the stress field near the crack tip. One parameter\nrepresents the stress intensity with classical unit of stress intensity\nfactors. It is interesting to find that the loading mode can be characterized\nby a length as the other parameter, which can properly reflect the phase of the\nstress oscillation with respect to the distance to the crack tip. This is quite\ndifferent from other crack tip fields in which the loading mode is usually\nexpressed by a phase angle. The corresponding failure criterion for interface\ncracks does not include any arbitrarily chosen quantity, and therefore is\nconvenient for comparing and accumulating experimental results, even existing\nones.", "category": "cond-mat_other" }, { "text": "Condon domains - these non-magnetic diamagnetic domains: The paper, not pretending for a complete and detailed review, is intended\nmainly for a wide community of physicists, not only specialists in this\nparticular subject. The author gives a physical picture of the periodic\nemergence of instabilities and well-known diamagnetic domains (Condon domains)\nin metals resulting from the strong de Haas-van Alphen effect. The most\nsignificant experiments on observation and study of the domain state in metals\nare described. In particular, the recent achievements in this area using muon\nspin rotation, as well as the amazing phenomenon of \"supersoftness\" observed in\nthe magnetostriction experiments, are presented. Novel, not previously\ndiscussed features of the phenomenon related to the metal compressibility are\nenlightened.", "category": "cond-mat_other" }, { "text": "La-dilution effects in TbRhIn5 antiferromagnet: We report measurements of temperature dependent magnetic susceptibility,\nresonant x-ray magnetic scattering (XRMS) and heat capacity on single crystals\nof Tb1-xLaxRhIn5 for nominal concentrations in the range 0.0 < x < 1.0. TbRhIn5\nis an antiferromagnetic (AFM) compound with TN ~ 46 K, which is the highest TN\nvalues along the RRhIn5 series. We explore the suppression of the\nantiferromagnetic (AFM) state as a function of La-doping considering the\neffects of La-induced dilution and perturbations to the tetragonal crystalline\nelectrical field (CEF) on the long range magnetic interaction between the\nTb$^{3+}$ ions. Additionally, we also discuss the role of disorder. Our results\nand analysis are compared to the properties of the undoped compound and of\nother members of the RRhIn5 family and structurally related compounds (R2RhIn8\nand RIn3). The XRMS measurements reveal that the commensurate magnetic\nstructure with the magnetic wave-vector (0,1/2,1/2) observed for the undoped\ncompound is robust against doping perturbations in Tb0.6La0.4RhIn5 compound.", "category": "cond-mat_other" }, { "text": "Magnetism and structure of magnetic multilayers based on the fully spin\n polarized Heusler alloys Co2MnGe and Co2MnSn: Our Introduction starts with a short general review of the magnetic and\nstructural properties of the Heusler compounds which are under discussion in\nthis book. Then, more specifically, we come to the discussion of our\nexperimental results on multilayers composed of the Heusler alloys Co2MnGe and\nCo2MnSn with V or Au as interlayers. The experimental methods we apply combine\nmagnetization and magneto-resistivity measurements, x-ray diffraction and\nreflectivity, soft x-ray magnetic circular dichroism and spin polarized neutron\nreflectivity. We find that below a critical thickness of the Heusler layers at\ntypically dcr = 1.5 nm the ferromagnetic order is lost and spin glass order\noccurs instead. For very thin ferromagnetic Heusler layers there are\npeculiarities in the magnetic order which are unusual when compared to\nconventional ferromagnetic transition metal multilayer systems. In [Co2MnGe/Au]\nmultilayers there is an exchange bias shift at the ferromagnetic hysteresis\nloops at low temperatures caused by spin glass ordering at the interface. In\n[Co2MnGe/V] multilayers we observe an antiferromagnetic interlayer long range\nordering below a well defined Neel temperature originating from the dipolar\nstray fields at the magnetically rough Heusler layer interfaces.", "category": "cond-mat_other" }, { "text": "Anomalous reflection and excitation of surface waves in metamaterials: We consider reflection of electromagnetic waves from layered structures with\nvarious dielectric and magnetic properties, including metamaterials. Assuming\nperiodic variations in the permittivity, we find that the reflection is in\ngeneral anomalous. In particular, we note that the specular reflection vanishes\nand that the incident energy is totally reflected in the backward direction,\nwhen the conditions for resonant excitation of leaking surface waves are\nfulfilled.", "category": "cond-mat_other" }, { "text": "Collective Excitations of Bose-Einstein Condensates in a Double-Well\n Potential: We investigate collective excitations of Bose-Einstein condensates at\nabsolute zero in a double-well trap. We solve the Bogoliubov equations with a\ndouble-well trap, and show that the crossover from the dipole mode to the\nJosephson plasma mode occurs in the lowest energy excitation. It is found that\nthe anomalous tunneling property of low energy excitations is crucial to the\ncrossover.", "category": "cond-mat_other" }, { "text": "Hydrodynamic theory of transport in doped graphene: We study non-linear dc transport in graphene using a hydrodynamic approach\nand conclude that in clean samples the drift velocity saturates at a weakly\ndensity-dependent value v_{sat} ~ 10^7 cm/s. We show that saturation results\nfrom the interactions between graphene's Dirac quasi-particles and both\nacoustic and optical phonons. Saturation is accompanied by substantial electron\nheating and is not reached at realistic driving fields in moderately or\nstrongly disordered samples. We find that it is essential to account for\ninteractions among graphene's Dirac quasi-particles, which increase the linear\nresponse resistivity at high temperatures or low densities.", "category": "cond-mat_other" }, { "text": "Axicon Lens for Coherent Matter Waves: We have realized a conical matter wave lens. The repulsive potential of a\nfocused laser beam was used to launch a Bose-Einstein condensate into a\nradially expanding wavepacket whose perfect ring shape was ensured by energy\nconservation. In spite of significant interactions between atoms, the spatial\nand velocity widths of the ring along its radial dimension remained extremely\nnarrow, as also confirmed by numerical simulations. Our results open the\npossibility for cylindrical atom optics without the perturbing effect of\nmean-field interactions.", "category": "cond-mat_other" }, { "text": "Analytical solution of the equation of motion for a rigid domain wall in\n a magnetic material with perpendicular anisotropy: This paper reports the solution of the equation of motion for a domain wall\nin a magnetic material which exhibits high magneto-crystalline anisotropy.\nStarting from the Landau-Lifschitz-Gilbert equation for field-induced motion,\nwe solve the equation to give an analytical expression, which specifies the\ndomain wall position as a function of time. Taking parameters from a Co/Pt\nmultilayer system, we find good quantitative agreement between calculated and\nexperimentally determined wall velocities, and show that high field uniform\nwall motion occurs when wall rigidity is assumed.", "category": "cond-mat_other" }, { "text": "Giant planar Hall effect in colossal magnetoresistive\n La(0.84)Sr(0.16)MnO(3) thin films: The transverse resistivity in thin films of La(0.84)Sr(0.16)MnO(3)\n(LSMO)exhibits sharp field-symmetric jumps below Tc. We show that a likely\nsource of this behavior is the giant planar Hall effect (GPHE) combined with\nbiaxial magnetic anisotropy. The effect is comparable in magnitude to that\nobserved recently in the magnetic semiconductor Ga(Mn)As. It can be potentially\nused in applications such as magnetic sensors and non-volatile memory devices.", "category": "cond-mat_other" }, { "text": "Coherent backscattering of Bose-Einstein condensates in two-dimensional\n disorder potentials: We study quantum transport of an interacting Bose-Einstein condensate in a\ntwo-dimensional disorder potential. In the limit of vanishing atom-atom\ninteraction, a sharp cone in the angle-resolved density of the scattered matter\nwave is observed, arising from constructive interference between amplitudes\npropagating along reversed scattering paths. Weak interaction transforms this\ncoherent backscattering peak into a pronounced dip, indicating destructive\ninstead of constructive interference. We reproduce this result, obtained from\nthe numerical integration of the Gross-Pitaevskii equation, by a diagrammatic\ntheory of weak localization in presence of a nonlinearity.", "category": "cond-mat_other" }, { "text": "Long-lived Feshbach molecules in a 3D optical lattice: We have created and trapped a pure sample of 87Rb2 Feshbach molecules in a\nthree-dimensional optical lattice. Compared to previous experiments without a\nlattice we find dramatic improvements such as long lifetimes of up to 700 ms\nand a near unit efficiency for converting tightly confined atom pairs into\nmolecules. The lattice shields the trapped molecules from collisions and thus\novercomes the problem of inelastic decay by vibrational quenching. Furthermore,\nwe have developed a novel purification scheme that removes residual atoms,\nresulting in a lattice in which individual sites are either empty or filled\nwith a single molecule in the vibrational ground state of the lattice.", "category": "cond-mat_other" }, { "text": "Auger mediated quantum sticking of positrons to surfaces: Evidence for\n single step transition from a scattering state to a surface image potential\n bound state: We present the observation of an efficient mechanism for positron sticking to\nsurfaces termed here Auger mediated quantum sticking. In this process the\nenergy associated with the positrons transition from an unbound scattering\nstate to a bound image potential state is coupled to a valence electron which\ncan then have sufficient energy to leave the surface. Compelling evidence for\nthis mechanism is found in a narrow secondary electron peak observed at\nincident positron kinetic energies well below the electron work function.", "category": "cond-mat_other" }, { "text": "Expansions of the interatomic potential for different boundary\n conditions and the transition to the thermodynamic limit: We analyze the possible expansions of the interatomic potential\n$U(|\\textbf{r}_{1}-\\textbf{r}_{2}|)$ in a Fourier series for a cyclic system\nand a system with boundaries. We also study the transition from exact\nexpansions for a finite system to the expansion that is commonly used in the\nthermodynamic limit. The analysis shows that such a transition distorts the\npotential of a bounded system by making it cyclic.", "category": "cond-mat_other" }, { "text": "Improvements in 3D Automated Shimming Techniques in High-Resolution NMR: Traditionally the improvement of static magnetic field homogeneity of the\nmagnet in Nuclear Magnetic Resonance (NMR) spectroscopy is performed manually,\nwhich has many limitations. However, in recent years a number of automated\nshimming techniques based on Fourier Imaging Technique have been proposed.\nExisting 3D automated shimming methods require special, Pulsed Field Gradient\n(PFG) hardware, which is not available on majority of high-resolution NMR\nspectrometers. The modified technique, presented in this thesis uses the normal\nNMR hardware provided with the majority of high-resolution NMR spectrometers.\nThe 3D shimming technique described was optimised for use with Varian UNITY\nINOVA spectrometers and successfully tested with both protonated and deuterated\nsolvents. A method for calibrating linear transverse shim field gradients and\ncorrecting any non-orthogonality and imbalance of strengths is proposed. The\neffect of thermal convection on field mapping was observed and is reported here\nfor the first time.", "category": "cond-mat_other" }, { "text": "Semiconductor-metal nanoparticle molecules: hybrid excitons and\n non-linear Fano effect: Modern nanotechnology opens the possibility of combining nanocrystals of\nvarious materials with very different characteristics in one superstructure.\nThe resultant superstructure may provide new physical properties not\nencountered in homogeneous systems. Here we study theoretically the optical\nproperties of hybrid molecules composed of semiconductor and metal\nnanoparticles. Excitons and plasmons in such a hybrid molecule become strongly\ncoupled and demonstrate novel properties. At low incident light intensity, the\nexciton peak in the absorption spectrum is broadened and shifted due to\nincoherent and coherent interactions between metal and semiconductor\nnanoparticles. At high light intensity, the absorption spectrum demonstrates a\nsurprising, strongly asymmetric shape. This shape originates from the coherent\ninter-nanoparticle Coulomb interaction and can be viewed as a non-linear Fano\neffect which is quite different from the usual linear Fano resonance.", "category": "cond-mat_other" }, { "text": "Observation of deviations from ideal gas thermodynamics in a trapped\n Bose-Einstein condensed gas: We have investigated experimentally the finite-temperature properties of a\nBose-Einstein condensed cloud of $^{87}$Rb atoms in a harmonic trap. Focusing\nprimarily on condensed fraction and expansion energy, we measure unambiguous\ndeviations from ideal-gas thermodynamics, and obtain good agreement with a\nHartree-Fock description of the mixed cloud. Our results offer for the first\ntime clear evidence of the mutual interaction between the condensed and thermal\ncomponents. To probe the low-temperature region unaccessible to the usual\ntime-of-flight technique, we use coherent Bragg scattering as a filtering\ntechnique for the condensate. This allows us to separate spatially the\ncondensed and normal components in time of flight, and to measure reliably\ntemperatures as low as $0.2 T_{\\rm c}^0$ and thermal fractions as low as\n10%.Finally, we observe evidence for the limitations of the usual image\nanalysis procedure, pointing out to the need for a more elaborate model of the\nexpansion of the mixed cloud.", "category": "cond-mat_other" }, { "text": "Transport of Atom Packets in a Train of Ioffe-Pritchard Traps: We demonstrate transport and evaporative cooling of several atomic clouds in\na chain of magnetic Ioffe-Pritchard traps moving at a low speed ($<1$~m/s). The\ntrapping scheme relies on the use of a magnetic guide for transverse\nconfinement and of magnets fixed on a conveyor belt for longitudinal trapping.\nThis experiment introduces a new approach for parallelizing the production of\nBose-Einstein condensates as well as for the realization of a continuous atom\nlaser.", "category": "cond-mat_other" }, { "text": "Superfluid Bose-Fermi mixture from weak-coupling to unitarity: We investigate the zero-temperature properties of a superfluid Bose-Fermi\nmixture by introducing a set of coupled Galilei-invariant nonlinear\nSchr\\\"odinger equations valid from weak-coupling to unitarity. The Bose\ndynamics is described by a Gross-Pitaevskii-type equation including\nbeyond-mean-field corrections possessing the correct weak-coupling and\nunitarity limits. The dynamics of the two-component Fermi superfluid is\ndescribed by a density-functional equation including beyond-mean-field terms\nwith correct weak-coupling and unitarity limits. The present set of equations\nis equivalent to the equations of generalized superfluid hydrodynamics, which\ntake into account also surface effects. The equations describe the mixture\nproperly as the Bose-Bose repulsive (positive) and Fermi-Fermi attractive\n(negative) scattering lengths are varied from zero to infinity in the presence\nof a Bose-Fermi interaction. The present model is tested numerically as the\nBose-Bose and Fermi-Fermi scattering lengths are varied over wide ranges\ncovering the weak-coupling to unitarity transition.", "category": "cond-mat_other" }, { "text": "Dynamics of localized spins coupled to the conduction electrons with\n charge/spin currents: The effects of the charge/spin currents of conduction electrons on the\ndynamics of the localized spins are studied in terms of the perturbation in the\nexchange coupling $J_{K}$ between them. The equations of motion for the\nlocalized spins are derived exactly up to $O(J_{K}^2)$, and the equations for\nthe two-spin system is solved numerically. It is found that the dynamics\ndepends sensitively upon the relative magnitude of the charge and spin\ncurrents, i.e., it shows steady state, periodic motion, and even chaotic\nbehavior. Extension to the multi-spin system and its implications including\npossible ``spin current detector'' are also discussed.", "category": "cond-mat_other" }, { "text": "Radio-frequency operation of a double-island single-electron transistor: We present results on a double-island single-electron transistor (DISET)\noperated at radio-frequency (rf) for fast and highly sensitive detection of\ncharge motion in the solid state. Using an intuitive definition for the charge\nsensitivity, we compare a DISET to a conventional single-electron transistor\n(SET). We find that a DISET can be more sensitive than a SET for identical,\nminimum device resistances in the Coulomb blockade regime. This is of\nparticular importance for rf operation where ideal impedance matching to 50 Ohm\ntransmission lines is only possible for a limited range of device resistances.\nWe report a charge sensitivity of 5.6E-6 e/sqrt(Hz) for a rf-DISET, together\nwith a demonstration of single-shot detection of small (<=0.1e) charge signals\non microsecond timescales.", "category": "cond-mat_other" }, { "text": "Exciton and biexciton energies in bilayer systems: We report calculations of the energies of excitons and biexcitons in ideal\ntwo-dimensional bilayer systems within the effective-mass approximation with\nisotropic electron and hole masses. The exciton energies are obtained by a\nsimple numerical integration technique, while the biexciton energies are\nobtained from diffusion quantum Monte Carlo calculations. The exciton binding\nenergy decays as the inverse of the separation of the layers, while the binding\nenergy of the biexciton with respect to dissociation into two separate excitons\ndecays exponentially.", "category": "cond-mat_other" }, { "text": "Artificial electromagnetism for neutral atoms: Escher staircase and\n Laughlin liquids: We show how lasers may create fields which couple to neutral atoms in the\nsame way that the electromagnetic fields couple to charged particles. These\nfields are needed for using neutral atoms as an analog quantum computer for\nsimulating the properties of many-body systems of charged particles. They allow\nfor seemingly paradoxical geometries, such as a ring where atoms continuously\nreduce their potential energy while moving in a closed path. We propose neutral\natom experiments which probe quantum Hall effects and the interplay between\nmagnetic fields and periodic potentials.", "category": "cond-mat_other" }, { "text": "Faraday waves in Bose-Einstein condensates: Motivated by recent experiments on Faraday waves in Bose-Einstein condensates\nwe investigate both analytically and numerically the dynamics of cigar-shaped\nBose-condensed gases subject to periodic modulation of the strength of the\ntransverse confinement. We offer a fully analytical explanation of the observed\nparametric resonance, based on a Mathieu-type analysis of the non-polynomial\nSchr{\\\"o}dinger equation. The theoretical prediction for the pattern\nperiodicity versus the driving frequency is directly compared with the\nexperimental data, yielding good qualitative and quantitative agreement between\nthe two. These results are corroborated by direct numerical simulations of both\nthe one-dimensional non-polynomial Schr{\\\"o}dinger equation and of the fully\nthree-dimensional Gross-Pitaevskii equation.", "category": "cond-mat_other" }, { "text": "Structural phase transitions in epitaxial perovskite films: Three different film systems have been systematically investigated to\nunderstand the effects of strain and substrate constraint on the phase\ntransitions of perovskite films. In SrTiO$_3$ films, the phase transition\ntemperature T$_C$ was determined by monitoring the superlattice peaks\nassociated with rotations of TiO$_6$ octahedra. It is found that T$_C$ depends\non both SrTiO$_3$ film thickness and SrRuO$_3$ buffer layer thickness. However,\nlattice parameter measurements showed no sign of the phase transitions,\nindicating that the tetragonality of the SrTiO$_3$ unit cells was no longer a\ngood order parameter. This signals a change in the nature of this phase\ntransition, the internal degree of freedom is decoupled from the external\ndegree of freedom. The phase transitions occur even without lattice relaxation\nthrough domain formation. In NdNiO$_3$ thin films, it is found that the\nin-plane lattice parameters were clamped by the substrate, while out-of-plane\nlattice constant varied to accommodate the volume change across the phase\ntransition. This shows that substrate constraint is an important parameter for\nepitaxial film systems, and is responsible for the suppression of external\nstructural change in SrTiO$_3$ and NdNiO$_3$ films. However, in SrRuO$_3$ films\nwe observed domain formation at elevated temperature through x-ray reciprocal\nspace mapping. This indicated that internal strain energy within films also\nplayed an important role, and may dominate in some film systems. The final\nstrain states within epitaxial films were the result of competition between\nmultiple mechanisms and may not be described by a single parameter.", "category": "cond-mat_other" }, { "text": "Theory of magnon-polaritons in quantum Ising materials: We present a theory of magnon-polaritons in quantum Ising materials, and\ndevelop a formalism describing the coupling between light and matter as an\nIsing system is tuned through its quantum critical point. The theory is applied\nto Ising materials having multilevel single-site Hamiltonians, in which\nmultiple magnon modes are present, such as the insulating Ising magnet\nLiHoF$_4$ . We find that the magnon-photon coupling strengths may be tuned by\nthe applied transverse field, with the coupling between the soft mode present\nin the quantum Ising material and a photonic resonator mode diverging at the\nquantum critical point of the material. A fixed system of spins will not\nexhibit the diamagnetic response expected when light is coupled to mobile spins\nor atoms. Without the diamagnetic response, one expects a divergent\nmagnon-photon coupling strength to lead to a superradiant quantum phase\ntransition. However, this neglects the effects of damping and decoherence\npresent in any real system. We show that damping and decoherence may block the\nsuperradiant quantum phase transition, and lead to weak coupling between the\nsoft magnon mode and the resonator mode. The results of the theory are applied\nto experimental data on the model system LiHoF$_4$ in a microwave resonator.", "category": "cond-mat_other" }, { "text": "Photoluminescence Spectroscopy of the Molecular Biexciton in Vertically\n Stacked Quantum Dot Pairs: We present photoluminescence studies of the molecular neutral\nbiexciton-exciton spectra of individual vertically stacked InAs/GaAs quantum\ndot pairs. We tune either the hole or the electron levels of the two dots into\ntunneling resonances. The spectra are described well within a few-level,\nfew-particle molecular model. Their properties can be modified broadly by an\nelectric field and by structural design, which makes them highly attractive for\ncontrolling nonlinear optical properties.", "category": "cond-mat_other" }, { "text": "Interference of spin states in photoemission from Sb/Ag(111): Using a three-dimensional spin polarimeter we have gathered evidence for the\ninterference of spin states in photoemission from the surface alloy Sb/Ag(111).\nThis system features a small Rashba-type spin-splitting of a size comparable to\nthe linewidth of the quasiparticles, thus causing an intrinsic overlap between\nstates with orthogonal spinors. Besides a small spin polarization caused by the\nspin-splitting, we observe a large spin polarization component in the plane\nnormal to the quantization axis provided by the Rashba effect. Strongly\nsuggestive of coherent spin rotation, this effect is largely independent of the\nphoton energy and photon polarization.", "category": "cond-mat_other" }, { "text": "Non-radiative exciton energy transfer in hybrid organic-inorganic\n heterostructures: Non-radiative optical energy transfer from a GaAs quantum well to a thin\noverlayer of an infrared organic semiconductor dye is unambiguously\ndemonstrated. The dynamics of exciton transfer are studied in the time-domain\nusing pump-probe spectroscopy at the donor site and fluorescence spectroscopy\nat the acceptor site. The effect is observed as simultaneous increase of the\npopulation decay rate at the donor and of the rise time of optical emission at\nthe acceptor sites. The hybrid configuration under investigation provides an\nalternative non-radiative, non-contact pumping route to electrical carrier\ninjection that overcomes the losses imposed by the associated low carrier\nmobility of organic emitters.", "category": "cond-mat_other" }, { "text": "Light scattering in Cooper-paired Fermi atoms: We present a detailed theoretical study of light scattering off superfluid\ntrapped Fermi gas of atoms at zero temperature. We apply Nambu-Gorkov formalism\nof superconductivity to calculate the response function of superfluid gas due\nto stimulated light scattering taking into account the final state\ninteractions. The polarization of light has been shown to play a significant\nrole in response of Cooper-pairs in the presence of a magnetic field.\nParticularly important is a scheme of polarization-selective light scattering\nby either spin-component of the Cooper-pairs leading to the single-particle\nexcitations of one spin-component only. These excitations have a threshold of\n$2\\Delta$ where $\\Delta$ is the superfluid gap energy. Furthermore,\npolarization-selective light scattering allows for unequal energy and momentum\ntransfer to the two partner atoms of a Cooper-pair. In the regime of low energy\n($<< 2\\Delta$) and low momentum ($<2\\Delta/(\\hbar v_F)$, $v_F$ being the Fermi\nvelocity) transfer, a small difference in momentum transfers to the two\nspin-components may be useful in exciting Bogoliubov-Anderson phonon mode. We\npresent detailed results on the dynamic structure factor (DSF) deduced from the\nresponse function making use of generalized fluctuation-dissipation theorem.\nModel calculations using local density approximation for trapped superfluid\nFermi gas shows that when the energy transfer is less than $2\\Delta_0$, where\n$\\Delta_0$ refers to the gap at the trap center, DSF as a function of energy\ntransfer has reduced gradient compared to that of normal Fermi gas.", "category": "cond-mat_other" }, { "text": "Epitaxial self-organization: from surfaces to magnetic materials: Self-organization of magnetic materials is an emerging and active field. An\noverview of the use of self-organization for magnetic purposes is given, with a\nview to illustrate aspects that cannot be covered by lithography. A first set\nof issues concerns the quantitative study of low-dimensional magnetic phenomena\n(1D and 0D). Such effects also occur in microstructured and\nlithographically-patterned materials but cannot be studied in these because of\nthe complexity of such materials. This includes magnetic ordering, magnetic\nanisotropy and superparamagnetism. A second set of issues concerns the\npossibility to directly use self-organization in devices. Two sets of examples\nare given: first, how superparamagnetism can be fought by fabricating thick\nself-organized structures, and second, what new or improved functionalities can\nbe expected from self-organized magnetic systems, like the tailoring of\nmagnetic anisotropy or controlled dispersion of properties.", "category": "cond-mat_other" }, { "text": "Characterization of the Shell Structure in Coupled Quantum Dots through\n Resonant Optical Probing: Excited states in single quantum dots (QDs) have been shown to be useful for\nspin state initialization and manipulation. For scalable quantum information\nprocessing it is necessary to have multiple spins interacting. Therefore, we\npresent initial results from photoluminescence excitation studies of excited\nstates in coupled quantum dots (CQDs). Due to the rich set of possible\nexcitation and recombination possibilities, a technique for visualizing\nphotoluminescence excitation in coupled quantum dots is discussed, by which\nboth the interaction between the dots and the type of absorption and emission\nthat generated the photoluminescence is easily and clearly revealed. As an\nexample, this technique is applied to characterize the shell structure of the\nhole in the top dot and the results are compared with those using Level\nAnti-Crossing Spectroscopy (LACS).", "category": "cond-mat_other" }, { "text": "Drift mobility of long-living excitons in coupled GaAs quantum wells: We observe high-mobility transport of indirect excitons in coupled GaAs\nquantum wells. A voltage-tunable in-plane potential gradient is defined for\nexcitons by exploiting the quantum confined Stark effect in combination with a\nlithographically designed resistive top gate. Excitonic photoluminescence\nresolved in space, energy, and time provides insight into the in-plane drift\ndynamics. Across several hundreds of microns an excitonic mobility of >10^5\ncm2/eVs is observed for temperatures below 10 K. With increasing temperature\nthe excitonic mobility decreases due to exciton-phonon scattering.", "category": "cond-mat_other" }, { "text": "The two-site Bose--Hubbard model: The two-site Bose--Hubbard model is a simple model used to study Josephson\ntunneling between two Bose--Einstein condensates. In this work we give an\noverview of some mathematical aspects of this model. Using a classical\nanalysis, we study the equations of motion and the level curves of the\nHamiltonian. Then, the quantum dynamics of the model is investigated using\ndirect diagonalisation of the Hamiltonian. In both of these analyses, the\nexistence of a threshold coupling between a delocalised and a self-trapped\nphase is evident, in qualitative agreement with experiments. We end with a\ndiscussion of the exact solvability of the model via the algebraic Bethe\nansatz.", "category": "cond-mat_other" }, { "text": "Suppressing the Kibble-Zurek mechanism by a symmetry-violating bias: The formation of topological defects in continuous phase transitions is\ndriven by the Kibble-Zurek mechanism. Here we study the formation of single-\nand half-quantum vortices during transition to the polar phase of $^3$He in the\npresence of a symmetry-breaking bias provided by the applied magnetic field. We\nfind that vortex formation is suppressed exponentially when the length scale\nassociated with the bias field becomes smaller than the Kibble-Zurek length. We\nthus demontrate an experimentally feasible shortcut to adiabaticity -- an\nimportant aspect for further understanding of phase transitions as well as for\nengineering applications such as quantum computers or simulators.", "category": "cond-mat_other" }, { "text": "Electromagnetic properties of graphene junctions: A resonant chiral tunneling (CT) across a graphene junction (GJ) induced by\nan external electromagnetic field (EF) is studied. Modulation of the electron\nand hole wavefunction phases $\\varphi$ by the external EF during the CT\nprocesses strongly impacts the CT directional diagram. Therefore the a.c.\ntransport characteristics of GJs depend on the EF polarization and frequency\nconsiderably. The GJ shows great promises for various nanoelectronic\napplications working in the THz diapason.", "category": "cond-mat_other" }, { "text": "Effective field theory for He-IV: We introduce an effective scalar field theory to describe the He-IV phase\ndiagram, which can be considered as a generalization of the XY model which\ngives the usual lambda-transition. This theory results from a Ginzburg-Landau\nHamiltonian with higher order derivatives, which allow to produce transitions\nbetween the superfluid, normal liquid and solid phases of He-IV. Mean field and\nMonte Carlo analyses suggest that this model is able to reproduce the main\nqualitative features of He-IV phase transitions.", "category": "cond-mat_other" }, { "text": "Polarisation rotation of slow light with orbital angular momentum in\n ultracold atomic gases: We consider the propagation of slow light with an orbital angular momentum\n(OAM) in a moving atomic medium. We have derived a general equation of motion\nand applied it in analysing propagation of slow light with an OAM in a rotating\nmedium, such as a vortex lattice. We have shown that the OAM of slow light\nmanifests itself in a rotation of the polarisation plane of linearly polarised\nlight. To extract a pure rotational phase shift, we suggest to measure a\ndifference in the angle of the polarisation plane rotation by two consecutive\nlight beams with opposite OAM. The differential angle $\\Delta\\alpha_{\\ell}$ is\nproportional to the rotation frequency of the medium $\\omega_{\\mathrm{rot}}$\nand the winding number $\\ell$ of light, and is inversely proportional to the\ngroup velocity of light. For slow light the angle $\\Delta\\alpha_{\\ell}$ should\nbe large enough to be detectable. The effect can be used as a tool for\nmeasuring the rotation frequency $\\omega_{\\mathrm{rot}}$ of the medium.", "category": "cond-mat_other" }, { "text": "Piezo-Magneto-Electric Effects in p-Doped Semiconductors: We predict the appearance of a uniform magnetization in strained three\ndimensional p-doped semiconductors with inversion symmetry breaking subject to\nan external electric field. We compute the magnetization response to the\nelectric field as a function of the direction and magnitude of the applied\nstrain. This effect could be used to manipulate the collective magnetic moment\nof hole mediated ferromagnetism of magnetically doped semiconductors.", "category": "cond-mat_other" }, { "text": "Radiative annihilation of a soliton and an antisoliton in the coupled\n sine-Gordon equation: In the sine-Gordon equation solitons and antisolitons in the absence of\nperturbations do not annihilate. Here I present numerical analysis of\nsoliton-antisoliton collisions in the coupled sine-Gordon equation. It is shown\nthat in such a system soliton-antisoliton pairs (breathers) do annihilate even\nin the absence of perturbations. The annihilation occurs via a\nlogarithmic-in-time decay of a breather caused by emission of plasma waves in\nevery period of breather oscillations. This also leads to a significant\ncoupling between breathers and propagating waves, which may lead to\nself-oscillations at the geometrical resonance conditions in a dc-driven\nsystem. The phenomenon may be useful for achieving superradiant emission from\ncoupled oscillators.", "category": "cond-mat_other" }, { "text": "Scattering of surface plasmon polaritons by one-dimensional\n inhomogeneities: The scattering of surface plasmons polaritons by a one-dimensional defect of\nthe surface is theoretically studied, by means of both Rayleigh and modal\nexpansions. The considered defects are either relief perturbations or\nvariations in the permittivity of the metal. The dependence of transmission,\nreflection and out-of-plane scattering on parameters defining the defect is\npresented. We find that the radiated energy is forwardly directed (with respect\nto the surface plasmon propagation) in the case of an impedance defect.\nHowever, for relief defects, the radiated energy may be directed into backward\nor forward (or both) directions, depending on the defect width.", "category": "cond-mat_other" }, { "text": "Pseudo-potential of a power-law decaying interaction in two-dimensional\n systems: We analytically derive the general pseudo-potential operator of an arbitrary\nisotropic interaction for particles confined in two-dimensional (2D) systems,\nusing the frame work developed by Huang and Yang for 3D scattering. We also\nanalytically derive the low energy dependence of the scattering phase-shift for\nan arbitrary interaction with a power-law decaying tail, $V_{\\rm\n2D}(\\rho)\\propto \\rho^{-\\alpha}$ (for $\\alpha>2$). We apply our results to the\n2D dipolar gases ($\\alpha=3$) as an example, calculating the momentum and\ndipole moment dependence of the pseudo-potential for both $s$- and p-wave\nscattering channels if the two scattering particles are in the same 2D layer.\nResults for the s-wave scattering between particles in two different (parallel)\nlayers are also investigated. Our results can be directly applied to the\nsystems of dipolar atoms and/or polar molecules in a general 2D geometry.", "category": "cond-mat_other" }, { "text": "Stochastic Dynamical Structure (SDS) of Nonequilibrium Processes in the\n Absence of Detailed Balance. IV: Emerging of Stochastic Dynamical Equalities\n and Steady State Thermodynamics from Darwinian Dynamics: This is the fourth paper, the last one, on solution to the problem of absence\nof detailed balance in nonequilibrium processes. It is an approach based on\nanother known universal dynamics: The evolutionary dynamics first conceived by\nDarwin and Wallace, referring to as Darwinian dynamics in the present paper,\nhas been found to be universally valid in biology; The statistical mechanics\nand thermodynamics, while enormously successful in physics, have been in an\nawkward situation of wanting a consistent dynamical understanding; Here we\npresent from a formal point of view an exploration of the connection between\nthermodynamics and Darwinian dynamics and a few related topics. We first show\nthat the stochasticity in Darwinian dynamics implies the existence temperature,\nhence the canonical distribution of Boltzmann-Gibbs type. In term of relative\nentropy the Second Law of thermodynamics is dynamically demonstrated without\ndetailed balance condition, and is valid regardless of size of the system. In\nparticular, the dynamical component responsible for breaking detailed balance\ncondition does not contribute to the change of the relative entropy. Two types\nof stochastic dynamical equalities of current interest are explicitly discussed\nin the present approach: One is based on Feynman-Kac formula and another is a\ngeneralization of Einstein relation. Both are directly accessible to\nexperimental tests. Our demonstration indicates that Darwinian dynamics\nrepresents logically a simple and straightforward starting point for\nstatistical mechanics and thermodynamics and is complementary to and consistent\nwith conservative dynamics that dominates the physical sciences. Present\nexploration suggests the existence of a unified stochastic dynamical framework\nboth near and far from equilibrium.", "category": "cond-mat_other" }, { "text": "Two-particle binding energy of interacting Bose gases: The pole of the two-particle T-matrix including the influence of the\nsurrounding medium is analyzed for an interacting Bose gas. The phase diagram\nof the Bose -Einstein condensation (BEC) depending on the temperature, density,\nscattering length, and momentum is derived from this pole. The critical\nmomentum for the occurrence of superfluidity is obtained in this way. As a new\nobservation a two- particle binding energy is reported intimately connected\nwith the occurrence of the BEC. It is suggested that this might have\ncosmological consequences on the dark energy problem.", "category": "cond-mat_other" }, { "text": "Hard Core Bosons on the Triangular Lattice at Zero Temperature: A Series\n Expansion Study: We use high order linked cluster series to investigate the hard core boson\nmodel on the triangular lattice, at zero temperature. Our expansions, in powers\nof the hopping parameter $t$, probe the spatially ordered `solid' phase and the\ntransition to a uniform superfluid phase. At the commensurate fillings $n=1/3,\n2/3$ we locate a quantum phase transition point at $(t/V)_c\\simeq 0.208(1)$, in\ngood agreement with recent Monte Carlo studies. At half-filling ($n=1/2$) we\nfind evidence for a solid phase, which persists to $t/V\\simeq 0.06$.", "category": "cond-mat_other" }, { "text": "Electron-spin beat susceptibility of excitons in semiconductor quantum\n wells: Recent time-resolved differential transmission and Faraday rotation\nmeasurements of long-lived electron spin coherence in quantum wells displayed\nintriguing parametric dependencies. For their understanding we formulate a\nmicroscopic theory of the optical response of a gas of optically incoherent\nexcitons whose constituent electrons retain spin coherence, under a weak\nmagnetic field applied in the quantum well's plane. We define a spin beat\nsusceptibility and evaluate it in linear order of the exciton density. Our\nresults explain the many-body physics underlying the basic features observed in\nthe experimental measurements.", "category": "cond-mat_other" }, { "text": "On the Energy-Based Variational Model for Vector Magnetic Hysteresis: We consider the quasi-static magnetic hysteresis model based on a\ndry-friction like representation of magnetization. The model has a consistent\nenergy interpretation, is intrinsically vectorial, and ensures a direct\ncalculation of the stored and dissipated energies at any moment in time, and\nhence not only on the completion of a closed hysteresis loop. We discuss the\nvariational formulation of this model and derive an efficient numerical scheme,\navoiding the usually employed approximation which can be inaccurate in the\nvectorial case. The parameters of this model for a nonoriented steel are\nidentified using a set of first order reversal curves. Finally, the model is\nincorporated as a local constitutive relation into a 2D finite element\nsimulation accounting for both the magnetic hysteresis and the eddy current.", "category": "cond-mat_other" }, { "text": "Energy flow of moving dissipative topological solitons: We study the energy flow due to the motion of topological solitons in\nnonlinear extended systems in the presence of damping and driving. The total\nfield momentum contribution to the energy flux, which reduces the soliton\nmotion to that of a point particle, is insufficient. We identify an additional\nexchange energy flux channel mediated by the spatial and temporal inhomogeneity\nof the system state. In the well-known case of a DC external force the\ncorresponding exchange current is shown to be small but non-zero. For the case\nof AC driving forces, which lead to a soliton ratchet, the exchange energy flux\nmediates the complete energy flow of the system. We also consider the case of\ncombination of AC and DC external forces, as well as spatial discretization\neffects.", "category": "cond-mat_other" }, { "text": "Nucleation at quantized vortices and the heterogeneous phase separation\n in supersaturated superfluid 3He-4He liquid mixtures: Supersaturated superfluid 3He-4He liquid mixture, separating into the\n3He-concentrated c-phase and 3He-diluted d-phase, represents a unique\npossibility for studying macroscopic quantum nucleation and quantum\nphase-separation kinetics in binary mixtures at low temperatures down to\nabsolute zero. One of possible heterogeneous mechanisms for the phase\nseparation of supersaturated d-phase is associated with superfluidity of this\nphase and with a possible existence of quantized vortices playing a role of\nnucleation sites for the c-phase of liquid mixture. We analyze the growth\ndynamics of vortex core filled with the c-phase and determine the temperature\nbehavior of c-phase nucleation rate and the crossover temperature between the\nclassical and quantum nucleation mechanisms.", "category": "cond-mat_other" }, { "text": "Logarithmic velocity profile of quantum turbulence of superfluid $^4$He: The logarithmic velocity profile is the most important statistical law of\nclassical turbulence affected by channel walls. This paper demonstrates\nnumerically that the logarithmic velocity profile of a superfluid flow appears\nin quantum turbulence under pure normal flow in a channel. We investigated the\nconfiguration and dynamics of an inhomogeneous vortex tangle affected by the\nwalls, and found the characteristic behavior of the log-law.", "category": "cond-mat_other" }, { "text": "Rayleigh-Taylor instability of crystallization waves at the\n superfluid-solid 4He interface: At the superfluid-solid 4He interface there exist crystallization waves\nhaving much in common with gravitational-capillary waves at the interface\nbetween two normal fluids. The Rayleigh-Taylor instability is an instability of\nthe interface which can be realized when the lighter fluid is propelling the\nheavier one. We investigate here the analogues of the Rayleigh-Taylor\ninstability for the superfluid-solid 4He interface. In the case of a uniformly\naccelerated interface the instability occurs only for a growing solid phase\nwhen the magnitude of the acceleration exceeds some critical value independent\nof the surface stiffness. For the Richtmyer-Meshkov limiting case of an\nimpulsively accelerated interface, the onset of instability does not depend on\nthe sign of the interface acceleration. In both cases the effect of\ncrystallization wave damping is to reduce the perturbation growth-rate of the\nTaylor unstable interface.", "category": "cond-mat_other" }, { "text": "Tunneling and Resonant Conductance in One-Dimensional Molecular\n Structures: We present a theory of tunneling and resonant transitions in one-dimensional\nmolecular systems which is based on Green's function theory of electron\nsub-barrier scattering off the structural units (or functional groups) of a\nmolecular chain. We show that the many-electron effects are of paramount\nimportance in electron transport and they are effectively treated using a\nformalism of sub-barrier scattering operators. The method which calculates the\ntotal scattering amplitude of the bridge molecule not only predicts the\nenhancement of the amplitude of tunneling transitions in course of tunneling\nelectron transfer through one-dimensional molecular structures but also allows\nus to interpret conductance mechanisms by calculating the bound energy spectrum\nof the tunneling electron, the energies being obtained as poles of the total\nscattering amplitude of the bridge molecule. We found that the resonant\ntunneling via bound states of the tunneling electron is the major mechanism of\nelectron conductivity in relatively long organic molecules. The sub-barrier\nscattering technique naturally includes a description of tunneling in applied\nelectric fields which allows us to calculate I-V curves at finite bias. The\ndeveloped theory is applied to explain experimental findings such as bridge\neffect due to tunneling through organic molecules, and threshold versus Ohmic\nbehavior of the conductance due to resonant electron transfer.", "category": "cond-mat_other" }, { "text": "Electronic Structure and Dynamics of Quantum-Well States in thin\n Yb-Metal Films: Quantum-well states above the Fermi energy in thin Yb(111)-metal films\ndeposited on a W(110) single crystal were studied by low-temperature scanning\ntunneling spectroscopy. These states are laterally highly localized and give\nrise to sharp peaks in the tunneling spectra. A quantitative analysis of the\nspectra yields the bulk-band dispersion in Gamma - L direction as well as\nquasi-particle lifetimes. The quadratic energy dependence of the lifetimes is\nin quantitative agreement with Fermi-liquid theory.", "category": "cond-mat_other" }, { "text": "Crystal truncation rods in kinematical and dynamical x-ray diffraction\n theories: Crystal truncation rods calculated in the kinematical approximation are shown\nto quantitatively agree with the sum of the diffracted waves obtained in the\ntwo-beam dynamical calculations for different reflections along the rod. The\nchoice and the number of these reflections are specified. The agreement extends\ndown to at least $\\sim 10^{-7}$ of the peak intensity. For lower intensities,\nthe accuracy of dynamical calculations is limited by truncation of the electron\ndensity at a mathematically planar surface, arising from the Fourier series\nexpansion of the crystal polarizability.", "category": "cond-mat_other" }, { "text": "Structure and magnetic properties of the Ho2Ge2O7 pyrogermanate: We report the anisotropic magnetic properties of Ho2Ge2O7 determined from dc\nand ac magnetization, specific heat and powder neutron diffraction experiments.\nThe magnetic lanthanide sublattice, seen in our refinement of the tetragonal\npyrogermanate crystal structure, is a right-handed spiral of edge-sharing and\ncorner-sharing triangles; the local Ho-O coordination indicates that the\ncrystal field is anisotropic. Susceptibility and magnetization data indeed show\nthat the magnetism is highly anisotropic, and the magnetic structure has the Ho\nmoments confined to the plane perpendicular to the structural spiral. The\nordered moment of Ho3+, as determined from refinement of the neutron\ndiffraction data, is 9.0 mu_B. Magnetic ordering occurs around 1.6 K.\nTemperature and field dependent ac susceptibility measurements show that this\ncompound displays spin relaxation phenomena analogous to what is seen in the\nspin ice pyrochlore system Ho2Ti2O7.", "category": "cond-mat_other" }, { "text": "Bragg spectroscopy of a strongly interacting Fermi gas: We present a comprehensive study of the Bose-Einstein condensate to\nBardeen-Cooper-Schrieffer (BEC-BCS) crossover in fermionic $^6$Li using Bragg\nspectroscopy. A smooth transition from molecular to atomic spectra is observed\nwith a clear signature of pairing at and above unitarity. These spectra probe\nthe dynamic and static structure factors of the gas and provide a direct link\nto two-body correlations. We have characterised these correlations and measured\ntheir density dependence across the broad Feshbach resonance at 834 G.", "category": "cond-mat_other" }, { "text": "Critical temperature of a trapped Bose gas: comparison of theory and\n experiment: We apply the Projected Gross-Pitaevskii equation (PGPE) formalism to the\nexperimental problem of the shift in critical temperature $T_c$ of a\nharmonically confined Bose gas as reported in Gerbier \\emph{et al.} [Phys. Rev.\nLett. \\textbf{92}, 030405 (2004)]. The PGPE method includes critical\nfluctuations and we find the results differ from various mean-field theories,\nand are in best agreement with experimental data. To unequivocally observe\nbeyond mean-field effects, however, the experimental precision must either\nimprove by an order of magnitude, or consider more strongly interacting\nsystems. This is the first application of a classical field method to make\nquantitative comparison with experiment.", "category": "cond-mat_other" }, { "text": "Entanglement between particle partitions in itinerant many-particle\n states: We review `particle partitioning entanglement' for itinerant many-particle\nsystems. This is defined as the entanglement between two subsets of particles\nmaking up the system. We identify generic features and mechanisms of particle\nentanglement that are valid over whole classes of itinerant quantum systems. We\nformulate the general structure of particle entanglement in many-fermion ground\nstates, analogous to the `area law' for the more usually studied entanglement\nbetween spatial regions. Basic properties of particle entanglement are first\nelucidated by considering relatively simple itinerant models. We then review\nparticle-partitioning entanglement in quantum states with more intricate\nphysics, such as anyonic models and quantum Hall states.", "category": "cond-mat_other" }, { "text": "Interference of a variable number of coherent atomic sources: We have studied the interference of a variable number of independently\ncreated $m_F=0$ microcondensates in a CO$_{2}$-laser optical lattice. The\nobserved average interference contrast decreases with condensate number N. Our\nexperimental results agree well with the predictions of a random walk model.\nWhile the exact result can be given in terms of Kluyver's formula, for a large\nnumber of sources a $1/\\sqrt{N}$ scaling of the average fringe contrast is\nobtained. This scaling law is found to be of more general applicability when\nquantifying the decay of coherence of an ensemble with N independently phased\nsources.", "category": "cond-mat_other" }, { "text": "Synchronized and Desynchronized Phases of Exciton-Polariton Condensates\n in the Presence of Disorder: Condensation of exciton-polaritons in semiconductor microcavities takes place\ndespite in plane disorder. Below the critical density the inhomogeneity of the\npotential seen by the polaritons strongly limits the spatial extension of the\nground state. Above the critical density, in presence of weak disorder, this\nlimitation is spontaneously overcome by the non linear interaction, resulting\nin an extended synchronized phase. This mechanism is clearly evidenced by\nspatial and spectral studies, coupled to interferometric measurements. In case\nof strong disorder, several non phase-locked (independent) condensates can be\nevidenced. The transition from synchronized phase to desynchronized phase is\naddressed considering multiple realizations of the disorder.", "category": "cond-mat_other" }, { "text": "Observation of Mass Transport through Solid 4He: By use of a novel experimental design, one that provides for superfluid\nhelium in contact with bulk hcp 4He off the melting curve, we have observed the\nDC transport of mass through a cell filled with solid 4He in the hcp region of\nthe phase diagram. Flow, which shows characteristics of a superflow, is seen to\nbe independent of the method used to grow the solid, but depends on pressure\nand temperature. The temperature dependence suggests the possibility of\nhysteresis.", "category": "cond-mat_other" }, { "text": "Spin Transfer Switching and Spin Polarization in Magnetic Tunnel\n Junctions with Mgo and Alox Barriers: We present spin transfer switching results for MgO based magnetic tunneling\njunctions (MTJs)with large tunneling magnetoresistance (TMR) ratio of up to\n150% and low intrinsic switching current density of 2-3 x 10 MA/cm2. The\nswitching data are compared to those obtained on similar MTJ nanostructures\nwith AlOx barrier. It is observed that the switching current density for MgO\nbased MTJs is 3-4 times smaller than that for AlOx based MTJs, and that can be\nattributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In\naddition, we report a qualitative study of TSP for a set of samples, ranging\nfrom 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at\nfinite bias) responsible for the current-driven magnetization switching is\nsuppressed as compared to zero-bias tunneling spin polarization determined from\nTMR.", "category": "cond-mat_other" }, { "text": "Rotational Analog of the Hall Effect: Coriolis Contribution to Electric\n Current: A galvanogyroscopic effect which is the rotational analog of the\ngravitomagnetic Hall effect has been proposed. As a consequence of Ohm's law in\nthe rotating frame, the effect of the Coriolis force on the conduction current\nis predicted to give rise to an azimuthal potential difference $V_{gg}$ about\n$10^{-3}V$ in a spinning rotor carrying radial electric current $i_r$. The\npotential difference developed by the galvanogyroscopic effect is proportional\nboth to angular velocity ${\\mathbf \\Omega}$ and to the electric current.", "category": "cond-mat_other" }, { "text": "Phase diagrams of the Bose-Hubbard model at finite temperature: The phase transitions in the Bose-Hubbard model are investigated. A\nsingle-particle Green's function is calculated in the random phase\napproximation and the formalism of the Hubbard operators is used. The regions\nof existence of the superfluid and Mott insulator phases are established and\nthe $(\\mu,t)$ (the chemical potential -- transfer parameter) phase diagrams are\nbuilt. The influence of temperature change on this transition is analyzed and\nthe phase diagram in the $(T,\\mu)$ plane is constructed. The role of thermal\nactivation of the ion hopping is investigated by taking into account the\ntemperature dependence of the transfer parameter. The reconstruction of the\nMott-insulator lobes due to this effect is analyzed.", "category": "cond-mat_other" }, { "text": "Charge qubit entanglement in double quantum dots: We study entanglement of charge qubits in a vertical tunnel-coupled double\nquantum dot containing two interacting electrons. Exact diagonalization is used\nto compute the negativity characterizing entanglement. We find that\nentanglement can be efficiently generated and controlled by sidegate voltages,\nand describe how it can be detected. For large enough tunnel coupling, the\nnegativity shows a pronounced maximum at an intermediate interaction strength\nwithin the Wigner molecule regime.", "category": "cond-mat_other" }, { "text": "Unusual magnetic behavior in ferrite hollow nanospheres: We report unusual magnetic behavior in iron oxide hollow nanospheres of 9.3\n$nm$ in diameter. The large fraction of atoms existing at the inner and outer\nsurfaces gives rise to a high magnetic disorder. The overall magnetic behavior\ncan be explained considering the coexistence of a soft superparamagnetic phase\nand a hard phase corresponding to the highly frustrated cluster-glass like\nphase at the surface regions.", "category": "cond-mat_other" }, { "text": "Dynamics of the quantum Duffing oscillator in the driving induced\n bistable regime: We investigate the nonlinear response of an anharmonic monostable quantum\nmechanical resonator to strong external periodic driving. The driving thereby\ninduces an effective bistability in which resonant tunneling can be identified.\nWithin the framework of a Floquet analysis, an effective Floquet-Born-Markovian\nmaster equation with time-independent coefficients can be established which can\nbe solved straightforwardly. Various effects including resonant tunneling and\nmulti-photon transitions will be described. Our model finds applications in\nnano-electromechanical devices such as vibrating suspended nano-wires as well\nas in non-destructive read-out procedures for superconducting quantum bits\ninvolving the nonlinear response of the read-out SQUID.", "category": "cond-mat_other" }, { "text": "Precision measurement of spin-dependent interaction strengths for spin-1\n and spin-2 87Rb atoms: We report on precision measurements of spin-dependent interaction-strengths\nin the 87Rb spin-1 and spin-2 hyperfine ground states. Our method is based on\nthe recent observation of coherence in the collisionally driven spin-dynamics\nof ultracold atom pairs trapped in optical lattices. Analysis of the Rabi-type\noscillations between two spin states of an atom pair allows a direct\ndetermination of the coupling parameters in the interaction hamiltonian. We\ndeduce differences in scattering lengths from our data that can directly be\ncompared to theoretical predictions in order to test interatomic potentials.\nOur measurements agree with the predictions within 20%. The knowledge of these\ncoupling parameters allows one to determine the nature of the magnetic ground\nstate. Our data imply a ferromagnetic ground state for 87Rb in the f=1\nmanifold, in agreement with earlier experiments performed without the optical\nlattice. For 87Rb in the f=2 manifold the data points towards an\nantiferromagnetic ground state, however our error bars do not exclude a\npossible cyclic phase.", "category": "cond-mat_other" }, { "text": "Plasma mechanisms of resonant terahertz detection in two-dimensional\n electron channel with split gates: We analyze the operation of a resonant detector of terahertz (THz) radiation\nbased on a two-dimensional electron gas (2DEG) channel with split gates. The\nside gates are used for the excitation of plasma oscillations by incoming THz\nradiation and control of the resonant plasma frequencies. The central gate\nprovides the potential barrier separating the source and drain portions of the\n2DEG channel. Two possible mechanisms of the detection are considered: (1)\nmodulation of the ac potential drop across the barrier and (2) heating of the\n2DEG due to the resonant plasma-assisted absorption of THz radiation followed\nby an increase in thermionic dc current through the barrier. Using the device\nmodel we calculate the frequency and temperature dependences of the detector\nresponsivity associated with both dynamic and heating (bolometric) mechanisms.\nIt is shown that the dynamic mechanisms dominates at elevated temperatures,\nwhereas the heating mechanism provides larger contribution at low temperatures,\nT=35-40 K.", "category": "cond-mat_other" }, { "text": "Kramers-Kronig constrained variational analysis of optical spectra: A universal method of extraction of the complex dielectric function\n$\\epsilon(\\omega)=\\epsilon_{1}(\\omega)+i\\epsilon_{2}(\\omega)$ from\nexperimentally accessible optical quantities is developed. The central idea is\nthat $\\epsilon_{2}(\\omega)$ is parameterized independently at each node of a\nproperly chosen anchor frequency mesh, while $\\epsilon_{1}(\\omega)$ is\ndynamically coupled to $\\epsilon_{2}(\\omega)$ by the Kramers-Kronig (KK)\ntransformation. This approach can be regarded as a limiting case of the\nmulti-oscillator fitting of spectra, when the number of oscillators is of the\norder of the number of experimental points. In the case of the normal-incidence\nreflectivity from a semi-infinite isotropic sample the new method gives\nessentially the same result as the conventional KK transformation of\nreflectivity. In contrast to the conventional approaches, the proposed\ntechnique is applicable, without readaptation, to virtually all types of\nlinear-response optical measurements, or arbitrary combinations of\nmeasurements, such as reflectivity, transmission, ellipsometry {\\it etc.}, done\non different types of samples, including thin films and anisotropic crystals.", "category": "cond-mat_other" }, { "text": "Quantum confinement corrections to the capacitance of gated\n one-dimensional nanostructures: With the help of a multi-configurational Green's function approach we\nsimulate single-electron Coulomb charging effects in gated ultimately scaled\nnanostructures which are beyond the scope of a selfconsistent mean-field\ndescription. From the simulated Coulomb-blockade characteristics we derive\neffective system capacitances and demonstrate how quantum confinement effects\ngive rise to corrections. Such deviations are crucial for the interpretation of\nexperimentally determined capacitances and the extraction of\napplication-relevant system parameters.", "category": "cond-mat_other" }, { "text": "Comment on \"Magnetic quantum oscillations of the conductivity in layered\n conductors\": We discuss the recent theory of Gvozdikov [Phys. Rev. B 70, 085113 (2004)]\nwhich aims at explaining the Shubnikov-de Haas oscillations of the longitudinal\nresistivity \\rho_zz observed in the quasi-two-dimensional organic compound\n\\beta''-(BEDT-TTF)_2SF_5CH_2CF_2SO_3.\n We point out that the self-consistent equations of the theory yielding the\nlongitudinal resistivity and the magnetic field dependence of the chemical\npotential have been incorrectly solved. We show that the consideration of the\nself-consistent Born approximation (which determines the relaxation rate in\nGvozdikov's paper) leads in fact to the complete absence of the longitudinal\nconductivity \\sigma_{zz} at leading order in high magnetic fields.", "category": "cond-mat_other" }, { "text": "Derivation of phenomenological expressions for transition matrix\n elements for electron-phonon scattering: In the literature on electron-phonon scatterings very often a\nphenomenological expression for the transition matrix element is used which was\nderived in the textbooks of Ashcroft/Mermin and of Czycholl. There are various\nsteps in the derivation of this expression. In the textbooks in part different\narguments have been used in these steps, but the final result is the same. In\nthe present paper again slightly different arguments are used which motivate\nthe procedure in a more intuitive way. Furthermore, we generalize the\nphenomenological expression to describe the dependence of the matrix elements\non the spin state of the initial and final electron state.", "category": "cond-mat_other" }, { "text": "Dislocation Mobility and Anomalous Shear Modulus Effect in $^4$He\n Crystals: We calculate the dislocation glide mobility in solid $^4$He within a model\nthat assumes the existence of a superfluid field associated with dislocation\nlines. Prompted by the results of this mobility calculation, we study within\nthis model the role that such a superfluid field may play in the motion of the\ndislocation line when a stress is applied to the crystal. To do this, we relate\nthe damping of dislocation motion, calculated in the presence of the assumed\nsuperfluid field, to the shear modulus of the crystal. As the temperature\nincreases, we find that a sharp drop in the shear modulus will occur at the\ntemperature where the superfluid field disappears. We compare the drop in shear\nmodulus of the crystal arising from the temperature dependence of the damping\ncontribution due to the superfluid field, to the experimental observation of\nthe same phenomena in solid $^4$He and find quantitative agreement. Our results\nindicate that such a superfluid field plays an important role in dislocation\npinning in a clean solid $^4$He at low temperatures and in this regime may\nprovide an alternative source for the unusual elastic phenomena observed in\nsolid $^4$He.", "category": "cond-mat_other" }, { "text": "Structural phase transitions in epitaxial perovskite films: Three different film systems have been systematically investigated to\nunderstand the effects of strain and substrate constraint on the phase\ntransitions of perovskite films. In SrTiO$_3$ films, the phase transition\ntemperature T$_C$ was determined by monitoring the superlattice peaks\nassociated with rotations of TiO$_6$ octahedra. It is found that T$_C$ depends\non both SrTiO$_3$ film thickness and SrRuO$_3$ buffer layer thickness. However,\nlattice parameter measurements showed no sign of the phase transitions,\nindicating that the tetragonality of the SrTiO$_3$ unit cells was no longer a\ngood order parameter. This signals a change in the nature of this phase\ntransition, the internal degree of freedom is decoupled from the external\ndegree of freedom. The phase transitions occur even without lattice relaxation\nthrough domain formation. In NdNiO$_3$ thin films, it is found that the\nin-plane lattice parameters were clamped by the substrate, while out-of-plane\nlattice constant varied to accommodate the volume change across the phase\ntransition. This shows that substrate constraint is an important parameter for\nepitaxial film systems, and is responsible for the suppression of external\nstructural change in SrTiO$_3$ and NdNiO$_3$ films. However, in SrRuO$_3$ films\nwe observed domain formation at elevated temperature through x-ray reciprocal\nspace mapping. This indicated that internal strain energy within films also\nplayed an important role, and may dominate in some film systems. The final\nstrain states within epitaxial films were the result of competition between\nmultiple mechanisms and may not be described by a single parameter.", "category": "cond-mat_other" }, { "text": "Magnetic monopoles in a charged two-condensate Bose-Einstein system: We propose that a charged two-condensate Bose system possesses point-like\ntopological defects which can be interpreted as magnetic monopoles. By making\nuse of the $\\phi$-mapping theory, the topological charges of these magnetic\nmonopoles can be expressed in terms of the Hopf indices and Brouwer degree of\nthe $\\phi$-mapping.", "category": "cond-mat_other" }, { "text": "Dynamical Exchange Interaction From Time-Dependent Spin Density\n Functional Theory: We report on {\\it ab initio} time-dependent spin dynamics simulations for a\ntwo-center magnetic molecular complex based on time-dependent non-collinear\nspin density functional theory. In particular, we discuss how the dynamical\nbehavior of the {\\it ab initio} spin-density in the time-domain can be mapped\nonto a model Hamiltonian based on the classical Heisenberg spin-spin\ninteraction $J\\vcr{S}_1\\cdot \\vcr{S}_2$. By analyzing individual localized-spin\ntrajectories, extracted from the spin-density evolution, we demonstrate a novel\nmethod for evaluating the effective Heisenberg exchange coupling constant, $J$,\nfrom first principles simulations. We find that $J$, extracted in such a new\ndynamical way, agrees quantitatively to that calculated by the standard density\nfunctional theory broken-symmetry scheme.", "category": "cond-mat_other" }, { "text": "Influence of s-d scattering on the electron density of states in\n ferromagnet/superconductor bilayer: We study the dependence of the electronic density of states (DOS) on the\ndistance from the boundary for a ferromagnet/superconductor bilayer. We\ncalculate the electron density of states in such structure taking into account\nthe two-band model of the ferromagnet (FM) with conducting s and localized d\nelectrons and a simple s-wave superconductor (SC). It is demonstrated that due\nto the electron s-d scattering in the ferromagnetic layer in the third order of\ns-d scattering parameter the oscillation of the density of states has larger\nperiod and more drastic decrease in comparison with the oscillation period for\nthe electron density of states in the zero order.", "category": "cond-mat_other" }, { "text": "Entanglement area law in superfluid $^4$He: Area laws were first discovered by Bekenstein and Hawking, who found that the\nentropy of a black hole grows proportional to its surface area, and not its\nvolume. Entropy area laws have since become a fundamental part of modern\nphysics, from the holographic principle in quantum gravity to ground state\nwavefunctions of quantum matter, where entanglement entropy is generically\nfound to obey area law scaling. As no experiments are currently capable of\ndirectly probing the entanglement area law in naturally occurring many-body\nsystems, evidence of its existence is based on studies of simplified theories.\nUsing new exact microscopic numerical simulations of superfluid $^4$He, we\ndemonstrate for the first time an area law scaling of entanglement entropy in a\nreal quantum liquid in three dimensions. We validate the fundamental principles\nunderlying its physical origin, and present an \"entanglement equation of state\"\nshowing how it depends on the density of the superfluid.", "category": "cond-mat_other" }, { "text": "Ground and excited-state fermions in a 1D double-well, exact and\n time-dependent density-functional solutions: Two of the most popular quantum mechanical models of interacting fermions are\ncompared to each other and to potentially exact solutions for a pair of\ncontact-interacting fermions trapped in a 1D double-well potential, a model of\natoms in a quasi-1D optical lattice or electrons of a Hydrogen molecule in a\nstrong magnetic field. An exact few-body Hamiltonian is solved numerically in\nmomentum space yielding a highly-correlated eigenspectrum. Additionally,\napproximate ground-state energies are obtained using both density functional\ntheory (DFT) functional and 2-site Hubbard models. A 1D adiabatic LDA kernel is\nconstructed for use in time-dependent density functional theory (TDDFT), and\nthe resulting excited-state spectrum is compared to the exact and Hubbard\nresults. DFT is shown to give accurate results for wells with small separations\nbut fails to describe localization of opposite spin fermions to different\nsites. A locally cognizant (LC) density functional based on an effective local\nfermion number would provide a solution to this problem, and an approximate\ntreatment presented here compares favorably with the exact and Hubbard results.\nThe TDDFT excited-state spectrum is accurate in the small parameter regime with\nnon-adiabatic effects accounting for any deviations. As expected, the\nground-state Hubbard model outperforms DFT at large separations but breaks down\nat intermediate separations due to improper scaling to the united-atom limit.\nAt strong coupling, both Hubbard and TDDFT methods fail to capture the\nappropriate energetics.", "category": "cond-mat_other" }, { "text": "Predicting scattering properties of ultracold atoms: adiabatic\n accumulated phase method and mass scaling: Ultracold atoms are increasingly used for high precision experiments that can\nbe utilized to extract accurate scattering properties. This calls for a\nstronger need to improve on the accuracy of interatomic potentials, and in\nparticular the usually rather inaccurate inner-range potentials. A boundary\ncondition for this inner range can be conveniently given via the accumulated\nphase method. However, in this approach one should satisfy two conditions,\nwhich are in principle conflicting, and the validity of these approximations\ncomes under stress when higher precision is required. We show that a better\ncompromise between the two is possible by allowing for an adiabatic change of\nthe hyperfine mixing of singlet and triplet states for interatomic distances\nsmaller than the separation radius. A mass scaling approach to relate\naccumulated phase parameters in a combined analysis of isotopically related\natom pairs is described in detail and its accuracy is estimated, taking into\naccount both Born-Oppenheimer and WKB breakdown. We demonstrate how numbers of\nsinglet and triplet bound states follow from the mass scaling.", "category": "cond-mat_other" }, { "text": "Optimal design of fast topological pumping: Utilizing synthetic dimensions generated by spatial or temporal modulation,\ntopological pumping enables the exploration of higher-dimensional topological\nphenomena through lower-dimensional physical systems. In this letter, we\npropose a rational design paradigm of fast topological pumping based on 1D and\n2D time-modulated discrete elastic lattices for the first time. Firstly, the\nrealization of topological pumping is ensured by introducing quantitative\nindicators to drive a transition of the edge or corner state in the lattice\nspectrum. Meanwhile, with the help of limiting speed for adiabaticity to\ncalculate the modulation time, a mathematical formulation of designing\ntopological pumping with the fastest modulation speed is presented. By applying\nthe proposed design paradigm, topological edge-bulk-edge and corner-bulk-corner\nenergy transport are successfully achieved, with 11.2 and 4.0 times of\nimprovement in modulation speed compared to classical pumping systems in the\nliterature. In addition, applying to 1D and 2D space-modulated systems, the\noptimized modulation schemes can reduce the number of stacks to 5.3% and 26.8%\nof the classical systems while ensuring highly concentrated energy transport.\nThis design paradigm is expected to be extended to the rational design of fast\ntopological pumping in other physical fields.", "category": "cond-mat_other" }, { "text": "Mapping Approach for Quantum-Classical Time Correlation Functions: The calculation of quantum canonical time correlation functions is considered\nin this paper. Transport properties, such as diffusion and reaction rate\ncoefficients, can be determined from time integrals of these correlation\nfunctions. Approximate, quantum-classical expressions for correlation\nfunctions, which are amenable to simulation, are derived. These expressions\nincorporate the full quantum equilibrium structure of the system but\napproximate the dynamics by quantum-classical evolution where a quantum\nsubsystem is coupled to a classical environment. The main feature of the\nformulation is the use of a mapping basis where the subsystem quantum states\nare represented by fictitious harmonic oscillator states. This leads to a full\nphase space representation of the dynamics that can be simulated without appeal\nto surface-hopping methods. The results in this paper form the basis for new\nsimulation algorithms for the computation of quantum transport properties of\nlarge many-body systems.", "category": "cond-mat_other" }, { "text": "Threshold behavior of bosonic two-dimensional few-body systems: Bosonic two-dimensional self-bound clusters consisting of $N$ atoms\ninteracting through additive van der Waals potentials become unbound at a\ncritical mass m*(N); m*(N) has been predicted to be independent of the size of\nthe system. Furthermore, it has been predicted that the ground state energy\nE(N) of the N-atom system varies exponentially as the atomic mass approaches\nm*. This paper reports accurate numerical many-body calculations that allow\nthese predictions to be tested. We confirm the existence of a universal\ncritical mass m*, and show that the near-threshold behavior can only be\ndescribed properly if a previously neglected term is included. We comment on\nthe universality of the energy ratio E(N+1)/E(N) near threshold.", "category": "cond-mat_other" }, { "text": "An Advice about Shimming in High-Resolution Nuclear Magnetic Resonance: Three methods of active shimming in high-resolution NMR in existence (manual\nshimming, lock optimization and gradient shimming) are briefly discussed and\ntheir advantages and shortcomings are compared and also an advice on their use\nis given.", "category": "cond-mat_other" }, { "text": "Atom-to-molecule conversion efficiency and adiabatic fidelity: The efficiency of converting two-species fermionic atoms into bosonic\nmolecules is investigated in terms of mean-field Lagrangian density. We find\nthat the STIRAP technique aided by Feshbach resonance is more effective than\nthe bare Fechbach resonance for $^6$Li atoms rather than $^{40}$K atoms. We\nalso make general consideration on the symmetry and its relevant conservation\nlaw, which enable us to introduce a natural definition of adiabatic fidelity\nfor CPT state. The calculated values of the fidelity then provide an\ninterpretation on why the conversion efficiencies for $^{40}$K and $^6$Li are\ndistinctly different.", "category": "cond-mat_other" }, { "text": "Exact BCS stochastic schemes for a time dependent many-body fermionic\n system: The exact quantum state evolution of a fermionic gas with binary interactions\nis obtained as the stochastic average of BCS-state trajectories. We find the\nmost general Ito stochastic equations which reproduce exactly the dynamics of\nthe system and we obtain some conditions to minimize the stochastic spreading\nof the trajectories in the Hilbert space. The relation between the optimized\nequations and mean-field equations is analyzed. The method is applied to a\nsimple two-site model. The simulations display effects that cannot be obtained\nin the mean-field approximation.", "category": "cond-mat_other" }, { "text": "Pairing mean-field theory for the dynamics of dissociation of molecular\n Bose-Einstein condensates: We develop a pairing mean-field theory to describe the quantum dynamics of\nthe dissociation of molecular Bose-Einstein condensates into their constituent\nbosonic or fermionic atoms. We apply the theory to one, two, and\nthree-dimensional geometries and analyze the role of dimensionality on the atom\nproduction rate as a function of the dissociation energy. As well as\ndetermining the populations and coherences of the atoms, we calculate the\ncorrelations that exist between atoms of opposite momenta, including the column\ndensity correlations in 3D systems. We compare the results with those of the\nundepleted molecular field approximation and argue that the latter is most\nreliable in fermionic systems and in lower dimensions. In the bosonic case we\ncompare the pairing mean-field results with exact calculations using the\npositive-$P$ stochastic method and estimate the range of validity of the\npairing mean-field theory. Comparisons with similar first-principle simulations\nin the fermionic case are currently not available, however, we argue that the\nrange of validity of the present approach should be broader for fermions than\nfor bosons in the regime where Pauli blocking prevents complete depletion of\nthe molecular condensate.", "category": "cond-mat_other" }, { "text": "A random matrix approach to detect defects in a strongly scattering\n polycrystal: how the memory effect can help overcome multiple scattering: We report on ultrasonic imaging in a random heterogeneous medium. The goal is\nto detect flaws embedded deeply into a polycrystalline material. A 64-element\narray of piezoelectric transmitters/receivers at a central frequency of 5 MHz\nis used to capture the Green's matrix in a backscattering configuration.\nBecause of multiple scattering, conventional imaging completely fails to detect\nthe deepest flaws. We utilize a random matrix approach, taking advantage of the\ndeterministic coherence of the backscattered wave-field which is characteristic\nof single scattering and related to the memory effect. This allows us to\nseparate single and multiple scattering contributions. As a consequence, we\nshow that flaws are detected beyond the conventional limit, as if multiple\nscattering had been overcome.", "category": "cond-mat_other" }, { "text": "Spinor condensates with a laser-induced quadratic Zeeman effect: We show that an effective quadratic Zeeman effect can be generated in\n$^{52}$Cr by proper laser configurations, and in particular by the dipole trap\nitself. The induced quadratic Zeeman effect leads to a rich ground-state phase\ndiagram, can be used to induce topological defects by controllably quenching\nacross transitions between phases of different symmetries, allows for the\nobservability of the Einstein-de Haas effect for relatively large magnetic\nfields, and may be employed to create $S=1/2$ systems with spinor dynamics.\nSimilar ideas could be explored in other atomic species opening an exciting new\ncontrol tool in spinor systems.", "category": "cond-mat_other" }, { "text": "Conversion Efficiencies of Heteronuclear Feshbach Molecules: We study the conversion efficiency of heteronuclear Feshbach molecules in\npopulation imbalanced atomic gases formed by ramping the magnetic field\nadiabatically. We extend the recent work [J. E. Williams et al., New J. Phys.,\n8, 150 (2006)] on the theory of Feshbach molecule formations to various\ncombinations of quantum statistics of each atomic component. A simple\ncalculation for a harmonically trapped ideal gas is in good agreement with the\nrecent experiment [S. B. Papp and C. E. Wieman, Phys. Rev. Lett., 97, 180404\n(2006)] without any fitting parameters. We also give the conversion efficiency\nas an explicit function of initial peak phase space density of the majority\nspecies for population imbalanced gases. In the low-density region where\nBose-Einstein condensation does not appear, the conversion efficiency is a\nmonotonic function of the initial peak phase space density, but independent of\nstatistics of a minority component. The quantum statistics of majority atoms\nhas a significant effect on the conversion efficiency. In addition,\nBose-Einstein condensation of an atomic component is the key element\ndetermining the maximum conversion efficiency.", "category": "cond-mat_other" }, { "text": "X-ray Coherent diffraction interpreted through the fractional Fourier\n transform: Diffraction of coherent x-ray beams is treated through the Fractionnal\nFourier transform. The transformation allow us to deal with coherent\ndiffraction experiments from the Fresnel to the Fraunhofer regime. The analogy\nwith the Huygens-Fresnel theory is first discussed and a generalized\nuncertainty principle is introduced.", "category": "cond-mat_other" }, { "text": "Hall Effect of Light: We derive the semiclassical equation of motion for the wave-packet of light\ntaking into account the Berry curvature in the momentum space. This equation\nnaturally describes the interplay between the orbital and spin angular momenta,\ni.e., the conservation of the total angular momentum of light. This leads to\nthe shift of the wave-packet motion perpendicular to the gradient of the\ndielectric constant, i.e., the polarization-dependent Hall effect of light. An\nenhancement of this effect in the photonic crystal is also proposed.", "category": "cond-mat_other" }, { "text": "Graphite vs graphene: scientific background: Nobel Prize in Physics 2010 was given for \"groundbreaking experiments\nregarding the two-dimensional material graphene.\" In fact, before graphene has\nbeen extracted from graphite and measured, some of its fundamental physical\nproperties have already been experimentally uncovered in bulk graphite. In this\nLetter to the Nobel Committee we propose to include those findings in the\nScientific Background", "category": "cond-mat_other" }, { "text": "Nonintegrable Schrodinger Discrete Breathers: In an extensive numerical investigation of nonintegrable translational motion\nof discrete breathers in nonlinear Schrodinger lattices, we have used a\nregularized Newton algorithm to continue these solutions from the limit of the\nintegrable Ablowitz-Ladik lattice. These solutions are shown to be a\nsuperposition of a localized moving core and an excited extended state\n(background) to which the localized moving pulse is spatially asymptotic. The\nbackground is a linear combination of small amplitude nonlinear resonant plane\nwaves and it plays an essential role in the energy balance governing the\ntranslational motion of the localized core. Perturbative collective variable\ntheory predictions are critically analyzed in the light of the numerical\nresults.", "category": "cond-mat_other" }, { "text": "Edge-localized states in quantum one-dimensional lattices: In one-dimensional quantum lattice models with open boundaries, we find and\nstudy localization at the lattice edge. We show that edge-localized eigenstates\ncan be found in both bosonic and fermionic systems, specifically, in the\nBose-Hubbard model with on-site interactions and in the spinless fermion model\nwith nearest-neighbor interactions. We characterize the localization through\nspectral studies via numerical diagonalization and perturbation theory, through\nconsiderations of the eigenfunctions, and through the study of explicit time\nevolution. We concentrate on few-particle systems, showing how more complicated\nedge states appear as the number of particles is increased.", "category": "cond-mat_other" }, { "text": "Dynamical Aspects of Analogue Gravity: The Backreaction of Quantum\n Fluctuations in Dilute Bose-Einstein Condensates: We discuss the backreaction force exerted by quantum fluctuations in dilute\nBose-Einstein condensates onto the motion of the classical background, derived\nby an ab initio approach from microscopic physics. It is shown that the\neffective-action method, widely employed in semiclassical quantum gravity,\nfails to give the full backreaction force. The failure of the effective-action\nmethod is traced back, inter alia, to the problem of the correct choice of the\nfundamental variables and the related operator ordering issues.", "category": "cond-mat_other" }, { "text": "Stability of Inhomogeneous Multi-Component Fermi Gases: Two-component equal-mass Fermi gases, in which unlike atoms interact through\na short-range two-body potential and like atoms do not interact, are stable\neven when the interspecies s-wave scattering length becomes infinitely large.\nSolving the many-body Schroedinger equation within a hyperspherical framework\nand by Monte Carlo techniques, this paper investigates how the properties of\ntrapped two-component gases change if a third or fourth component are added. If\nall interspecies scattering lengths are equal and negative, our calculations\nsuggest that both three- and four-component Fermi gases become unstable for a\ncertain critical set of parameters. The relevant length scale associated with\nthe collapse is set by the interspecies scattering length and we argue that the\ncollapse is, similar to the collapse of an attractive trapped Bose gas, a\nmany-body phenomenon. Furthermore, we consider a three-component Fermi gas in\nwhich two interspecies scattering lengths are negative while the other\ninterspecies scattering length is zero. In this case, the stability of the\nFermi system is predicted to depend appreciably on the range of the underlying\ntwo-body potential. We find parameter combinations for which the system appears\nto become unstable for a finite negative scattering length and parameter\ncombinations for which the system appears to be made up of weakly-bound trimers\nthat consist of one fermion of each species.", "category": "cond-mat_other" }, { "text": "Interferences in the density of two Bose-Einstein condensates consisting\n of identical or different atoms: The density of two {\\it initially independent} condensates which are allowed\nto expand and overlap can show interferences as a function of time due to\ninterparticle interaction. Two situations are separately discussed and\ncompared: (1) all atoms are identical and (2) each condensate consists of a\ndifferent kind of atoms. Illustrative examples are presented.", "category": "cond-mat_other" }, { "text": "Adiabatic Transport of Bose-Einstein Condensate in Double- and\n Triple-Well Traps: By using a close similarity between multi-photon and tunneling population\ntransfer schemes, we propose robust adiabatic methods for the transport of\nBose-Einstein condensate (BEC) in double- and triple-well traps. The\ncalculations within the mean-field approximation (Gross-Pitaevskii equation)\nshow that irreversible and complete transport takes place even in the presence\nof the non-linear effects caused by interaction between BEC atoms. The transfer\nis driven by adiabatic time-dependent monitoring the barriers and well depths.\nThe proposed methods are universal and can be applied to a variety of systems\nand scenarios.", "category": "cond-mat_other" }, { "text": "Three-Body Recombination of Identical Bosons with a Large Positive\n Scattering Length at Nonzero Temperature: For identical bosons with a large scattering length, the dependence of the\n3-body recombination rate on the collision energy is determined in the\nzero-range limit by universal functions of a single scaling variable. There are\nsix scaling functions for angular momentum zero and one scaling function for\neach higher partial wave. We calculate these universal functions by solving the\nSkorniakov--Ter-Martirosian equation. The results for the 3-body recombination\nas a function of the collision energy are in good agreement with previous\nresults from solving the 3-body Schroedinger equation for 4He atoms. The\nuniversal scaling functions can be used to calculate the 3-body recombination\nrate at nonzero temperature. We obtain an excellent fit to the data from the\nInnsbruck group for 133Cs atoms with a large positive scattering length.", "category": "cond-mat_other" }, { "text": "Beyond the locality approximation in the standard diffusion Monte Carlo\n method: We present a way to include non local potentials in the standard Diffusion\nMonte Carlo method without using the locality approximation. We define a\nstochastic projection based on a fixed node effective Hamiltonian, whose lowest\nenergy is an upper bound of the true ground state energy, even in the presence\nof non local operators in the Hamiltonian. The variational property of the\nresulting algorithm provides a stable diffusion process, even in the case of\ndivergent non local potentials, like the hard-core pseudopotentials. It turns\nout that the modification required to improve the standard Diffusion Monte\nCarlo algorithm is simple.", "category": "cond-mat_other" }, { "text": "On applicability of differential mixing rules for statistically\n homogeneous and isotropic dispersions: The classical differential mixing rules are assumed to be independent\neffective-medium approaches, applicable to certain classes of systems. In the\npresent work, the inconsistency of differential models for macroscopically\nhomogeneous and isotropic systems is illustrated with a model for the effective\npermittivity of simple dielectric systems of impenetrable balls. The analysis\nis carried out in terms of the compact group approach reformulated in a way\nthat allows one to analyze the role of different contributions to the\npermittivity distribution in the system. It is shown that the asymmetrical\nBruggeman model (ABM) is physically inconsistent since the electromagnetic\ninteraction between previously added constituents and those being added is\nreplaced by the interaction of the latter with recursively formed effective\nmedium. The overall changes in the effective permittivity due to addition of\none constituent include the contributions from both constituents and depend on\nthe system structure before the addition. Ignoring the contribution from one of\nthe constituents, we obtain generalized versions of the original ABM mixing\nrules. They still remain applicable only in a certain concentration ranges, as\nis shown with the Hashin-Shtrikman bounds. The results obtained can be\ngeneralized to macroscopically homogeneous and isotropic systems with complex\npermittivities of constituents.", "category": "cond-mat_other" }, { "text": "Reptation quantum Monte Carlo for lattice Hamiltonians with a\n directed-update scheme: We provide an extension to lattice systems of the reptation quantum Monte\nCarlo algorithm, originally devised for continuous Hamiltonians. For systems\naffected by the sign problem, a method to systematically improve upon the\nso-called fixed-node approximation is also proposed. The generality of the\nmethod, which also takes advantage of a canonical worm algorithm scheme to\nmeasure off-diagonal observables, makes it applicable to a vast variety of\nquantum systems and eases the study of their ground-state and excited-states\nproperties. As a case study, we investigate the quantum dynamics of the\none-dimensional Heisenberg model and we provide accurate estimates of the\nground-state energy of the two-dimensional fermionic Hubbard model.", "category": "cond-mat_other" }, { "text": "Joule expansion of a pure many-body state: We derive the Joule expansion of an isolated perfect gas from the principles\nof quantum mechanics. Contrary to most studies of irreversible processes which\nconsider composite systems, the gas many-body Hilbert space cannot be\nfactorised into Hilbert spaces corresponding to interesting and ignored degrees\nof freedom. Moreover, the expansion of the gas into the entire accessible\nvolume is obtained for pure states. Still, the number particle density is\ncharacterised by a chemical potential and a temperature. We discuss the special\ncase of a boson gas below the Bose condensation temperature.", "category": "cond-mat_other" }, { "text": "Chirality dependence of the radial breathing phonon mode density in\n single wall carbon nanotubes: A mass and spring model is used to calculate the phonon mode dispersion for\nsingle wall carbon nanotubes (SWNTs) of arbitrary chirality. The calculated\ndispersions are used to determine the chirality dependence of the radial\nbreathing phonon mode (RBM) density. Van Hove singularities, usually discussed\nin the context of the single particle electronic excitation spectrum, are found\nin the RBM density of states with distinct qualitative differences for zig zag,\narmchair and chiral SWNTs. The influence the phonon mode density has on the two\nphonon resonant Raman scattering cross-section is discussed.", "category": "cond-mat_other" }, { "text": "Polarized emission of GaN/AlN quantum dots : single dot spectroscopy and\n symmetry-based theory: We report micro-photoluminescence studies of single GaN/AlN quantum dots\ngrown along the (0001) crystal axis by molecular beam epitaxy on Si(111)\nsubstrates. The emission lines exhibit a linear polarization along the growth\nplane, but with varying magnitudes of the polarization degree and with\nprincipal polarization axes that do not necessarily correspond to\ncrystallographic directions. Moreover, we could not observe any splitting of\npolarized emission lines, at least within the spectral resolution of our setup\n(1 meV). We propose a model based on the joint effects of electron-hole\nexchange interaction and in-plane anisotropy of strain and/or quantum dot\nshape, in order to explain the quantitative differences between our\nobservations and those previously reported on, e.g. CdTe- or InAs-based quantum\ndots.", "category": "cond-mat_other" }, { "text": "Self-consistent theory for molecular instabilities in a normal\n degenerate Fermi gas in the BEC-BCS crossover: We investigate within a self-consistent theory the molecular instabilities\narising in the normal state of a homogeneous degenerate Fermi gas, covering the\nwhole BEC-BCS crossover. These are the standard instability for molecular\nformation, the BCS instability which corresponds to the formation of Cooper\npairs and the related Bose-Einstein instability. These instabilities manifest\nthemselves in the properties of the particle-particle vertex, which we\ncalculate in a ladder approximation. To find the critical temperatures\ncorresponding to these various instabilities, we handle the properties of the\ninteracting Fermi gas on the same footing as the instabilities by making use of\nthe same vertex. This approximate treatment is shown to be quite satisfactory\nin a number of limiting situations where it agrees with known exact results.\nThe results for the BCS critical temperature and for the BE condensation are\nfound to be in fair agreement with earlier results. The threshold for formation\nof molecules at rest undergoes a sizeable shift toward the BEC side, due to\nquantum effects arising from the presence of the degenerate Fermi gas. This\nshould make its experimental observation fairly easy. This shift remains\nimportant at least up to temperatures comparable to the Fermi energy of the\ngas.", "category": "cond-mat_other" }, { "text": "Dynamic Many-Body Theory. II. Dynamics of Strongly Correlated Fermi\n Fluids: We develop a systematic theory of multi-particle excitations in strongly\ninteracting Fermi systems. Our work is the generalization of the time-honored\nwork by Jackson, Feenberg, and Campbell for bosons, that provides, in its most\nadvanced implementation, quantitative predictions for the dynamic structure\nfunction in the whole experimentally accessible energy/momentum regime. Our\nview is that the same physical effects -- namely fluctuations of the wave\nfunction at an atomic length scale -- are responsible for the correct\nenergetics of the excitations in both Bose and Fermi fluids. Besides a\ncomprehensive derivation of the fermion version of the theory and discussion of\nthe approximations made, we present results for homogeneous He-3 and electrons\nin three dimensions. We find indeed a significant lowering of the zero sound\nmode in He-3 and a broadening of the collective mode due to the coupling to\nparticle-hole excitations in good agreement with experiments. The most visible\neffect in electronic systems is the appearance of a ``double-plasmon''\nexcitation.", "category": "cond-mat_other" }, { "text": "Work functions of self-assembled monolayers on metal surfaces: Using first-principles calculations we show that the work function of noble\nmetals can be decreased or increased by up to 2 eV upon the adsorption of\nself-assembled monolayers of organic molecules. We identify the contributions\nto these changes for several (fluorinated) thiolate molecules adsorbed on\nAg(111), Au(111) and Pt(111) surfaces. The work function of the clean metal\nsurfaces increases in this order, but adsorption of the monolayers reverses the\norder completely. Bonds between the thiolate molecules and the metal surfaces\ngenerate an interface dipole, whose size is a function of the metal, but it is\nrelatively independent of the molecules. The molecular and bond dipoles can\nthen be added to determine the overall work function.", "category": "cond-mat_other" }, { "text": "Counter-flow Induced Decoupling in Super-Fluid Turbulence: In mechanically driven superfluid turbulence the mean velocities of the\nnormal- and superfluid components are known to coincide: $\\mathbf U_{\\text{n}}\n=\\mathbf U_{\\text{s}}$. Numerous laboratory, numerical and analytical studies\nshowed that under these conditions the mutual friction between the normal- and\nsuperfluid velocity components couples also their fluctuations: $\\mathbf\nu'_{\\text{n}}(\\mathbf r,t) \\approx \\mathbf u'_{\\text{s}}(\\mathbf r,t)$ almost\nat all scales. In this paper we show that this is not the case in thermally\ndriven superfluid turbulence; here the counterflow velocity $\\mathbf\nU_{\\text{ns}}\\equiv \\mathbf U_{\\text{n}} -\\mathbf U_{\\text{s}}\\ne 0$. We\nsuggest a simple analytic model for the cross correlation function\n$\\left\\langle \\mathbf u'_{\\text{n}}(\\mathbf r,t) \\cdot \\mathbf\nu'_{\\text{s}}(\\mathbf r',t)\\right \\rangle$ and its dependence on\n$U_{\\text{ns}}$. We demonstrate that $\\mathbf u'_{\\text{n}}(\\mathbf r,t)$ and $\n\\mathbf u'_{\\text{s}}(\\mathbf r,t)$ are decoupled almost in the entire range of\nseparations $|\\mathbf r-\\mathbf r'|$ between the energy containing scale and\nintervortex distance.", "category": "cond-mat_other" }, { "text": "On the probable wave nature of Bose crystals: At the present time, it is considered that Bose crystals are formed at the\ncooling of a fluid, because the state of crystal is more favorable by energy.\nIt is also believed [1,2] that no ordering factor forming a crystal is present,\nexcept for the interatomic interaction.\n However, the available solutions [1,2,3] for the wave functions (WFs) of the\nground and excited states of a crystal are approximate and are obtained for\ncyclic boundary conditions, which are not realized in the Nature. Here, we\npresent the exact solutions for the WFs of a Bose crystal with rectangular\nlattice under natural zero boundary conditions.\n The structure of WFs implies that 1) a crystal is formed by a standing wave\nin the probability field; 2) a crystal in the ground state contains a\ncondensate of atoms with the wave vector \\textbf{k}_l=(\\pi/\\bar{R}_x,\n\\pi/\\bar{R}_y, \\pi/\\bar{R}_z) (\\bar{R}_x, \\bar{R}_y, \\bar{R}_z are the periods\nof the lattice) that is equal to a half of the vector of the reciprocal\nlattice. These solutions indicate that the ordering factor forming a crystal is\nan intense standing wave similar to a sound one. Thus, the periodicity of a\nlattice is caused by that of a sound wave, but not only by the energy minimum\nprinciple. Apparently, the crystals of other types and with different lattices\nhave the wave nature as well. The condensate opens a possibility to explain the\nnonclassical inertia moment discovered by Kim and Chan [4,5] in solid He-4,\nwhich testifies, probably, to the presence of a superfluid subsystem in the\ncrystal.", "category": "cond-mat_other" }, { "text": "Phase reciprocity of spin-wave excitation by a microstrip antenna: Using space-, time- and phase-resolved Brillouin light scattering\nspectroscopy we investigate the difference in phase of the two\ncounterpropagating spin waves excited by the same microwave microstrip\ntransducer. These studies are performed both for backward volume magnetostatic\nwaves and magnetostatic surface waves in an in-plane magnetized yttrium iron\ngarnet film. The experiments show that for the backward volume magnetostatic\nspin waves (which are reciprocal and excited symmetrically in amplitude) there\nis a phase difference of $\\pi$ associated with the excitation process and thus\nthe phase symmetry is distorted. On the contrary, for the magnetostatic surface\nspin waves (which are non-reciprocal and unsymmetrical in amplitude) the phase\nsymmetry is preserved (there is no phase difference between the two waves\nassociated with the excitation). Theoretical analysis confirms this effect.", "category": "cond-mat_other" }, { "text": "Quantum multimode model of elastic scattering from Bose Einstein\n condensates: Mean field approximation treats only coherent aspects of the evolution of a\nBose Einstein condensate. However, in many experiments some atoms scatter out\nof the condensate. We study an analytic model of two counter-propagating atomic\nGaussian wavepackets incorporating dynamics of incoherent scattering processes.\nWithin the model we can treat processes of elastic collision of atoms into the\ninitially empty modes, and observe how, with growing occupation, the bosonic\nenhancement is slowly kicking in. A condition for bosonic enhancement effect is\nfound in terms of relevant parameters. Scattered atoms form a squeezed state\nthat can be viewed as a multi-component condensate. Not only are we able to\ncalculate the dynamics of mode occupation, but also the full statistics of\nscattered atoms.", "category": "cond-mat_other" }, { "text": "Negative refraction in nonlinear wave systems: People have been familiar with the phenomenon of wave refraction for several\ncenturies. Recently, a novel type of refraction, i.e., negative refraction,\nwhere both incident and refractory lines locate on the same side of the normal\nline, has been predicted and realized in the context of linear optics in the\npresence of both right- and left-handed materials. In this work, we reveal, by\ntheoretical prediction and numerical verification, negative refraction in\nnonlinear oscillatory systems. We demonstrate that unlike what happens in\nlinear optics, negative refraction of nonlinear waves does not depend on the\npresence of the special left-handed material, but depends on suitable physical\ncondition. Namely, this phenomenon can be observed in wide range of oscillatory\nmedia under the Hopf bifurcation condition. The complex Ginzburg-Landau\nequation and a chemical reaction-diffusion model are used to demonstrate the\nfeasibility of this nonlinear negative refraction behavior in practice.", "category": "cond-mat_other" }, { "text": "Peculiarities in the properties of some rare-earth compounds with\n orthorhombic structures: Rare-earth manganites are fascinating, because they display a wide variety of\nfundamental properties from magnetism to ferroelectricity, from colossal\nmagnetoresistance to semi-metallicity, and because they can be used in a number\nof important technological applications such as controlling a magnetic memory\nby an electric field or vice versa, new types of attenuators or transducers\netc. In this paper, we present our investigation on monocrystal samples with an\northorhombic structure, grown in two different space groups: D2h(16) for\nLa0.78Pb0.22MnO3 and Pr0.7Sr0.3MnO3 and D2h(9) for HoMn2O5 and TbMn2O5. The\ndoped perovskite manganites Ln1-x Ax MnO3 (where Ln is a rare-earth ion and A\nis a divalent ion) from the group D2h(16), which crystallized in different\nmodifications of the perovskite structure, characterized by the parameter\ndeformation of the type c/√2k0 and a pure inverse cascade form -3 at k0.37 Tc and with strong mutual friction,\nwe observed numerically and confirmed analytically the scale-invariant spectrum\n$E(k)~ k^{-x}$ with a (k-independent) exponent x > 3 that gradually increases\nwith the temperature and reaches a value $x\\simeq 9$ for $T\\approx 0.72 Tc$. In\nthe near-critical regimes we discover a strong enhancement of intermittency\nwhich exceeds by an order of magnitude the corresponding level in classical\nhydrodynamic turbulence.", "category": "cond-mat_other" }, { "text": "Spin dynamics characterization in magnetic dots: The spin structure in a magnetic dot, which is an example of a quantum\nfew-body system, is studied as a function of exchange coupling strength and dot\nsize with in the semiclassical approximation on a discrete lattice. As the\nexchange coupli ng is decreased or the size is increased, the ground state\nundergoes a phase cha nge from a single domain ferromagnet to a spin vortex.\nThe line separating these two phases has been calculated numerically for small\nsystem sizes. %, and analytically for larger dots. The dipolar interaction has\nbeen fully included in our calculations. Magnon frequencies in such a dot have\nalso been calculated in both phases by the linearized equation of motion\nmethod. These results have also been reproduced f rom the Fourier transform of\nthe spin autocorrelation function. From the magnon Density Of States (DOS), it\nis possible to identify the magnetic phase of the dot. Furthermore, the magnon\nmodes have been characterized for both the ferromagnetic and the vortex phase,\nand the magnon instability mechanism leading to the vortex-ferro transition has\nalso been identified. The results can also be used to compute finite\ntemperature magnetization or vort icity of magnetic dots.", "category": "cond-mat_other" }, { "text": "Bistability in a magnetic and nonmagnetic double-quantum-well structure\n mediated by the magnetic phase transition: The hole distribution in a double quantum well (QW) structure consisting of a\nmagnetic and a nonmagnetic semiconductor QW is investigated as a function of\ntemperature, the energy shift between the QWs, and other relevant parameters.\nWhen the itinerant holes mediate the ferromagnetic ordering, it is shown that a\nbistable state can be formed through hole redistribution, resulting in a\nsignificant change in the properties of the constituting magnetic QW (i.e., the\nparamagnetic-ferromagnetic transition). The model calculation also indicates a\nlarge window in the system parameter space where the bistability is possible.\nHence, this structure could form the basis of a stable memory element that may\nbe scaled down to a few hole regime.", "category": "cond-mat_other" }, { "text": "Theoretical Analysis of Functionally Graded Piezoelectric Thick-walled\n Cylinder Subjected to Mechanical and Electric Loadings: In this paper, the theoretical analysis for a hollow thick-walled\nfunctionally graded piezoelectric cylinder subjected to electric and mechanical\nloads are developed. The cylinder consists of two materials (PZT4 and PVDF) and\nthe volume fraction of PZT4 is given in the three variable parameters power law\nform. By using the Voigt method and the assumption of a uniform strain field\nwithin the two linear elastic constituents, the complex hypergeometric\ndifferential equation of the radial displacement is obtained. Then the\nsolutions of the radial displacement, the stresses, and the electric potential\nare derived and solved. The method in this paper is more suitable for actual\nengineering gradient piezoelectric materials, and the volume fraction function\ncan cover more complicated situations. Finally, the influence of the parameter\nn in volume fraction on the mechanical behaviors are investigated, and the\ndifference between the circumferential and radial stresses is discussed to\nreduce the stress concentration in the functionally graded piezoelectric\ncylinder.", "category": "cond-mat_other" }, { "text": "Density Matrix Renormalization Group for Dummies: We describe the Density Matrix Renormalization Group algorithms for time\ndependent and time independent Hamiltonians. This paper is a brief but\ncomprehensive introduction to the subject for anyone willing to enter in the\nfield or write the program source code from scratch.", "category": "cond-mat_other" }, { "text": "Quantum complementarity of microcavity polaritons: We present an experiment that probes polariton quantum correlations by\nexploiting quantum complementarity. Specifically, we find that polaritons in\ntwo distinct idler-modes interfere if and only if they share the same\nsignal-mode so that \"which-way\" information cannot be gathered. The\nexperimental results prove the existence of polariton pair correlations that\nstore the \"which-way\" information. This interpretation is confirmed by a\ntheoretical analysis of the measured interference visibility in terms of\nquantum Langevin equations.", "category": "cond-mat_other" }, { "text": "Creating a supersolid in one-dimensional Bose mixtures: We identify a one-dimensional supersolid phase in a binary mixture of\nnear-hardcore bosons with weak, local inter-species repulsion. We find\nrealistic conditions under which such a phase, defined here as the coexistence\nof quasi-superfluidity and quasi-charge density wave order, can be produced and\nobserved in finite ultra-cold atom systems in a harmonic trap. Our analysis is\nbased on Luttinger liquid theory supported with numerical calculations using\nthe time-evolving block decimation method. Clear experimental signatures of\nthese two orders can be found, respectively, in time-of-flight interference\npatterns, and the structure factor S(k) derived from density correlations.", "category": "cond-mat_other" }, { "text": "Stability of superfluid and supersolid phases of dipolar bosons in\n optical lattices: We perform a stability analysis of superfluid (SF) and supersolid (SS) phases\nof polarized dipolar bosons in two-dimensional optical lattices at high filling\nfactors and zero temperature, and obtain the phase boundaries between SF,\ncheckerboard SS (CSS), striped SS (SSS), and collapse. We show that the phase\ndiagram can be explored through the application of an external field and the\ntuning of its direction with respect to the optical lattice plane. In\nparticular, we find a transition between the CSS and SSS phases.", "category": "cond-mat_other" }, { "text": "Frenkel-Kontorova model with cold trapped ions: We study analytically and numerically the properties of one-dimensional chain\nof cold ions placed in a periodic potential of optical lattice and global\nharmonic potential of a trap. In close similarity with the Frenkel-Kontorova\nmodel, a transition from sliding to pinned phase takes place with the increase\nof the optical lattice potential for the density of ions incommensurate with\nthe lattice period. Quantum fluctuations lead to a quantum phase transition and\nmelting of pinned instanton glass phase at large values of dimensional Planck\nconstant. The obtained results are also relevant for a Wigner crystal placed in\na periodic potential.", "category": "cond-mat_other" }, { "text": "Pure spin current from one-photon absorption of linearly polarized light\n in noncentrosymmetric semiconductors: We show that one-photon absorption of linearly polarized light should produce\npure spin currents in noncentrosymmetric semiconductors, including even bulk\nGaAs. We present 14x14 k.p model calculations of the effect in GaAs, including\nstrain, and pseudopotential calculations of the effect in wurtzite CdSe.", "category": "cond-mat_other" }, { "text": "First-principles calculation of the Gilbert damping parameter via the\n linear response formalism with application to magnetic transition-metals and\n alloys: A method for the calculations of the Gilbert damping parameter $\\alpha$ is\npresented, which based on the linear response formalism, has been implemented\nwithin the fully relativistic Korringa-Kohn-Rostoker band structure method in\ncombination with the coherent potential approximation alloy theory. To account\nfor thermal displacements of atoms as a scattering mechanism, an alloy-analogy\nmodel is introduced. This allows the determination of $\\alpha$ for various\ntypes of materials, such as elemental magnetic systems and ordered magnetic\ncompounds at finite temperature, as well as for disordered magnetic alloys at\n$T = 0$ K and above. The effects of spin-orbit coupling, chemical and\ntemperature induced structural disorder are analyzed. Calculations have been\nperformed for the 3$d$ transition-metals bcc Fe, hcp Co, and fcc Ni, their\nbinary alloys bcc Fe$_{1-x}$Co$_{x}$, fcc Ni$_{1-x}$Fe$_x$, fcc\nNi$_{1-x}$Co$_x$ and bcc Fe$_{1-x}$V$_{x}$, and for 5d impurities in\ntransition-metal alloys. All results are in satisfying agreement with\nexperiment.", "category": "cond-mat_other" }, { "text": "Aharonov-Bohm interferences from local deformations in graphene: One of the most interesting aspects of graphene is the tied relation between\nstructural and electronic properties. The observation of ripples in the\ngraphene samples both free standing and on a substrate has given rise to a very\nactive investigation around the membrane-like properties of graphene and the\norigin of the ripples remains as one of the most interesting open problems in\nthe system. The interplay of structural and electronic properties is\nsuccessfully described by the modelling of curvature and elastic deformations\nby fictitious gauge fields that have become an ex- perimental reality after the\nsuggestion that Landau levels can form associated to strain in graphene and the\nsubsequent experimental confirmation. Here we propose a device to detect\nmicrostresses in graphene based on a scanning-tunneling-microscopy setup able\nto measure Aharonov-Bohm inter- ferences at the nanometer scale. The\ninterferences to be observed in the local density of states are created by the\nfictitious magnetic field associated to elastic deformations of the sample.", "category": "cond-mat_other" }, { "text": "Electron-nuclear spin dynamics of Ga$^{2+}$ paramagnetic centers probed\n by spin dependent recombination: A master equation approach: Similar to nitrogen-vacancy centers in diamond and impurity atoms in silicon,\ninterstitial gallium deep paramagnetic centers in GaAsN have been proven to\nhave useful characteristics for the development of spintronic devices. Among\nother interesting properties, under circularly polarized light, gallium centers\nin GaAsN act as spin filters that dynamically polarize free and bound electrons\nreaching record spin polarizations (100\\%). Furthermore, the recent observation\nof the amplification of the spin filtering effect under a Faraday configuration\nmagnetic field has suggested that the hyperfine interaction that couples bound\nelectrons and nuclei permits the optical manipulation of its nuclear spin\npolarization. Even though the mechanisms behind the nuclear spin polarization\nin gallium centers are fairly well understood, the origin of nuclear spin\nrelaxation and the formation of an Overhauser-like magnetic field remain\nelusive. In this work we develop a model based on the master equation approach\nto describe the evolution of electronic and nuclear spin polarizations of\ngallium centers interacting with free electrons and holes. Our results are in\ngood agreement with existing experimental observations. In regard to the\nnuclear spin relaxation, the roles of nuclear dipolar and quadrupolar\ninteractions are discussed. Our findings show that, besides the hyperfine\ninteraction, the spin relaxation mechanisms are key to understand the\namplification of the spin filtering effect and the appearance of the\nOverhauser-like magnetic field. Based on our model's results we propose an\nexperimental protocol based on time resolved spectroscopy. It consists of a\npump-probe photoluminescence scheme that would allow the detection and the\ntracing of the electron-nucleus flip-flops through time resolved PL\nmeasurements.", "category": "cond-mat_other" }, { "text": "Comment on \"Critique of the foundations of time-dependent density\n functional theory\" [Phys. Rev.A. 75, 022513 (2007)]: A recent paper (Phys. Rev A. 75, 022513 (2007), arXiv:cond-mat/0602020)\nchallenges exact time-dependent density functional theory (TDDFT) on several\ngrounds. We explain why these criticisms are either irrelevant or incorrect,\nand that TDDFT is both formally exact and predictive.", "category": "cond-mat_other" }, { "text": "Spin Seebeck Effect: Amplification of Spin Waves by Thermal Torque: We observe amplification of spin-wave packets propagating along a film of\nyttrium iron garnet (YIG) subject to a transverse temperature gradient. The\namplification is attributed to a spin-transfer thermal torque created by spin\ncurrents generated by means of the spin Seebeck effect that acts on the\nmagnetization and opposes the relaxation. The experimental data are interpreted\nwith a simple theoretical model using spin-wave theory that gives an\namplification gain in very good agreement with measurements.", "category": "cond-mat_other" }, { "text": "Fundamental limits for non-destructive measurement of a single spin by\n Faraday rotation: Faraday rotation being a dispersive effect, is commonly considered as the\nmethod of choice for non-destructive detection of spin states. Nevertheless\nFaraday rotation is inevitably accompanied by spin-flips induced by Raman\nscattering, which compromises non-destructive detection. Here, we derive an\nexplicit general relation relating the Faraday rotation and the spin-flip Raman\nscattering cross-sections, from which precise criteria for non-destructive\ndetection are established. It is shown that, even in ideal conditions,\nnon-destructive measurement of a single spin can be achieved only in\nanisotropic media, or within an optical cavity.", "category": "cond-mat_other" }, { "text": "Deuteron Momentum Distribution in KD2HPO4: The momentum distribution in KD2PO4(DKDP) has been measured using neutron\nCompton scattering above and below the weakly first order\nparaelectric-ferroelectric phase transition(T=229K). There is very litte\ndifference between the two distributions, and no sign of the coherence over two\nlocations for the proton observed in the paraelectric phase, as in KH2PO4(KDP).\nWe conclude that the tunnel splitting must be much less than 20mev. The width\nof the distribution indicates that the effective potential for DKDP is\nsignificantly softer than that for KDP. As electronic structure calculations\nindicate that the stiffness of the potential increases with the size of the\ncoherent region locally undergoing soft mode fluctuations, we conclude that\nthere is a mass dependent quantum coherence length in both systems.", "category": "cond-mat_other" }, { "text": "Are high-energy photoemission final states free-electron-like?: Three-dimensional (3D) electronic band structure is fundamental for\nunderstanding a vast diversity of physical phenomena in solid-state systems,\nincluding topological phases, interlayer interactions in van der Waals\nmaterials, dimensionality-driven phase transitions, etc. Interpretation of\nARPES data in terms of 3D electron dispersions is commonly based on the\nfree-electron approximation for the photoemission final states. Our soft-X-ray\nARPES data on Ag metal reveals, however, that even at high excitation energies\nthe final states can be a way more complex, incorporating several Bloch waves\nwith different out-of-plane momenta. Such multiband final states manifest\nthemselves as a complex structure and excessive broadening of the spectral\npeaks from 3D electron states. We analyse the origins of this phenomenon, and\ntrace it to other materials such as Si and GaN. Our findings are essential for\naccurate determination of the 3D band structure over a wide range of materials\nand excitation energies in the ARPES experiment.", "category": "cond-mat_other" }, { "text": "A consistent description of the iron dimer spectrum with a correlated\n single-determinant wave function: We study the iron dimer by using an accurate ansatz for quantum chemical\ncalculations based on a simple variational wave function, defined by a single\ngeminal expanded in molecular orbitals and combined with a real space\ncorrelation factor. By means of this approach we predict that, contrary to\nprevious expectations, the neutral ground state is $^7 \\Delta$ while the ground\nstate of the anion is $^8 \\Sigma_g^-$, hence explaining in a simple way a long\nstanding controversy in the interpretation of the experiments. Moreover, we\ncharacterize consistently the states seen in the photoemission spectroscopy by\nLeopold \\emph{et al.}. It is shown that the non-dynamical correlations included\nin the geminal expansion are relevant to correctly reproduce the energy\nordering of the low-lying spin states.", "category": "cond-mat_other" }, { "text": "Intense slow beams of bosonic potassium isotopes: We report on an experimental realization of a two-dimensional magneto-optical\ntrap (2D-MOT) that allows the generation of cold atomic beams of 39K and 41K\nbosonic potassium isotopes. The high measured fluxes up to 1.0x10^11 atoms/s\nand low atomic velocities around 33 m/s are well suited for a fast and reliable\n3D-MOT loading, a basilar feature for new generation experiments on\nBose-Einstein condensation of dilute atomic samples. We also present a simple\nmultilevel theoretical model for the calculation of the light-induced force\nacting on an atom moving in a MOT. The model gives a good agreement between\npredicted and measured flux and velocity values for our 2D-MOT.", "category": "cond-mat_other" }, { "text": "Chiral charge-density-waves: We discovered the chirality of charge density waves (CDW) in 1T-TiSe$_2$ by\nusing scanning tunnelling microscopy (STM) and optical ellipsometry. We found\nthat the CDW intensity becomes $I{a_1}:I{a_2}:I{a_3} = 1:0.7 \\pm 0.1:0.5 \\pm\n0.1$, where $Ia_i$ (i =1, 2, 3) is the amplitude of the tunnelling current\ncontributed by the CDWs. There were two states, in which the three intensity\npeaks of the CDW decrease \\textit{clockwise} and \\textit{anticlockwise} when we\nindex each nesting vector in order of intensity in the Fourier transformation\nof the STM images. The chirality in CDW results in the three-fold symmetry\nbreaking. Macroscopically, two-fold symmetry was indeed observed in optical\nmeasurement. We propose the new generalized CDW chirality $H_{CDW} \\equiv\n{\\boldmath $q_1$} \\cdot ({\\boldmath $q_2$}\\times {\\boldmath $q_3$})$, where\n${\\boldmath $q_i$}$ are the nesting vectors, which is independent of the\nsymmetry of components. The nonzero $H_{CDW}$ - the triple-${\\boldmath $q$}$\nvectors do not exist in an identical plane in the reciprocal space - should\ninduce a real-space chirality in CDW system.", "category": "cond-mat_other" }, { "text": "Spectroscopy of Strong-Pulse Superradiance in a Bose-Einstein condensate: We study experimentally superradiance in a Bose-Einstein condensate using a\ntwo-frequency pump beam. By controlling the frequency difference between the\nbeam components, we measure the spectrum of the backward (energy-mismatched)\nsuperradiant atomic modes. In addition, we show that the populations of these\nmodes display coherent time-dynamics. These results are compared to a\nsemi-classical model based on coupled Schroedinger-Maxwell equations.", "category": "cond-mat_other" }, { "text": "Thermal Fluctuations of the Electric Field in the Presence of Carrier\n Drift: We consider a semiconductor in a non-equilibrium steady state, with a dc\ncurrent. On top of the stationary carrier motion there are fluctuations. It is\nshown that the stationary motion of the carriers (i.e., their drift) can have a\nprofound effect on the electromagnetic field fluctuations in the bulk of the\nsample as well as outside it, close to the surface (evanescent waves in the\nnear field). The effect is particularly pronounced near the plasma frequency.\nThis is because drift leads to a significant modification of the dispersion\nrelation for the bulk and surface plasmons.", "category": "cond-mat_other" }, { "text": "Topological Constraints on the Charge Distributions for the Thomson\n Problem: The method of Morse theory is used to analyze the distributions of unit\ncharges interacting through a repulsive force and constrained to move on the\nsurface of a sphere -- the Thomson problem. We find that, due to topological\nreasons, the system may organize itself in the form of pentagonal structures.\nThis gives a qualitative account for the interesting ``pentagonal buttons''\ndiscovered in recent numerical work.", "category": "cond-mat_other" }, { "text": "Combined chips for atom-optics: We present experiments with Bose-Einstein condensates on a combined atom\nchip. The combined structure consists of a large-scale \"carrier chip\" and\nsmaller \"atom-optics chips\", containing micron-sized elements. This allows us\nto work with condensates very close to chip surfaces without suffering from\nfragmentation or losses due to thermally driven spin flips. Precise\nthree-dimensional positioning and transport with constant trap frequencies are\ndescribed. Bose-Einstein condensates were manipulated with submicron accuracy\nabove atom-optics chips. As an application of atom chips, a direction sensitive\nmagnetic field microscope is demonstrated.", "category": "cond-mat_other" }, { "text": "Quantum Non-Demolition Detection of Strongly Correlated Systems: Preparation, manipulation, and detection of strongly correlated states of\nquantum many body systems are among the most important goals and challenges of\nmodern physics. Ultracold atoms offer an unprecedented playground for\nrealization of these goals. Here we show how strongly correlated states of\nultracold atoms can be detected in a quantum non-demolition scheme, that is, in\nthe fundamentally least destructive way permitted by quantum mechanics. In our\nmethod, spatially resolved components of atomic spins couple to quantum\npolarization degrees of freedom of light. In this way quantum correlations of\nmatter are faithfully mapped on those of light; the latter can then be\nefficiently measured using homodyne detection. We illustrate the power of such\nspatially resolved quantum noise limited polarization measurement by applying\nit to detect various standard and \"exotic\" types of antiferromagnetic order in\nlattice systems and by indicating the feasibility of detection of superfluid\norder in Fermi liquids.", "category": "cond-mat_other" }, { "text": "Energy flow of moving dissipative topological solitons: We study the energy flow due to the motion of topological solitons in\nnonlinear extended systems in the presence of damping and driving. The total\nfield momentum contribution to the energy flux, which reduces the soliton\nmotion to that of a point particle, is insufficient. We identify an additional\nexchange energy flux channel mediated by the spatial and temporal inhomogeneity\nof the system state. In the well-known case of a DC external force the\ncorresponding exchange current is shown to be small but non-zero. For the case\nof AC driving forces, which lead to a soliton ratchet, the exchange energy flux\nmediates the complete energy flow of the system. We also consider the case of\ncombination of AC and DC external forces, as well as spatial discretization\neffects.", "category": "cond-mat_other" }, { "text": "Comparison study of DFA and DMA methods in analysis of autocorrelations\n in time series: Statistics of the Hurst scaling exponents calculated with the use of two\nmethods: recently introduced Detrended Moving Average Analysis(DMA) and\nDetrended Fluctuation Analysis (DFA)are compared. Analysis is done for\nartificial stochastic Brownian time series of various length and reveals\ninteresting statistical relationships between two methods. Good agreement\nbetween DFA and DMA techniques is found for long time series $L\\sim 10^{5}$,\nhowever for shorter series we observe that two methods give different results\nwith no systematic relation between them. It is shown that, on the average, DMA\nmethod overestimates the Hurst exponent comparing it with DFA technique.", "category": "cond-mat_other" }, { "text": "Quantum dynamics of two bosons in an anharmonic trap: Collective vs\n internal excitations: This work deals with the effects of an anharmonic trap on an interacting\ntwo-boson system in one dimension. Our primary focus is on the role of the\ninduced coupling between the center of mass and the relative motion as both\nanharmonicity and the (repulsive) interaction strength are varied. The ground\nstate reveals a strong localization in the relative coordinate, counteracting\nthe tendency to fragment for stronger repulsion. To explore the quantum\ndynamics, we study the system's response upon (i) exciting the harmonic ground\nstate by continuously switching on an additional anharmonicity, and (ii)\ndisplacing the center of mass, this way triggering collective oscillations. The\ninterplay between collective and internal dynamics materializes in the collapse\nof oscillations, which are explained in terms of few-mode models.", "category": "cond-mat_other" }, { "text": "Temporal dynamics of tunneling. Hydrodynamic approach: We use the hydrodynamic representation of the Gross -Pitaevskii/Nonlinear\nSchroedinger equation in order to analyze the dynamics of macroscopic tunneling\nprocess. We observe a tendency to a wave breaking and shock formation during\nthe early stages of the tunneling process. A blip in the density distribution\nappears in the outskirts of the barrier and under proper conditions it may\ntransform into a bright soliton. Our approach, based on the theory of shock\nformation in solutions of Burgers equation, allows us to find the parameters of\nthe ejected blip (or soliton if formed) including the velocity of its\npropagation. The blip in the density is formed regardless of the value and sign\nof the nonlinearity parameter. However a soliton may be formed only if this\nparameter is negative (attraction) and large enough. A criterion is proposed.\nAn ejection of a soliton is also observed numerically. We demonstrate,\ntheoretically and numerically, controlled formation of soliton through\ntunneling. The mass of the ejected soliton is controlled by the initial state.", "category": "cond-mat_other" }, { "text": "Nonlinear intraband tunneling of BEC in a cubic three-dimensional\n lattice: The intra-band tunneling of a Bose-Einstein condensate between three\ndegenerate high-symmetry X-points of the Brillouin zone of a cubic optical\nlattice is studied in the quantum regime by reduction to a three-mode model.\nThe mean-field approximation of the deduced model is described. Compared to the\npreviously reported two-dimensional (2D) case [Phys. Rev. A 75, 063628 (2007)],\nwhich is reducible to the two-mode model, in the case under consideration there\nexist a number of new stable stationary atomic distributions between the\nX-points and a new critical lattice parameter. The quantum collapses and\nrevivals of the atomic population dynamics are absent for the experimentally\nrealizable time span. The 2D stationary configurations, embedded into the 3D\nlattice, turn out to be always unstable, while existence of a stable 1D\ndistribution, where all atoms populate only one X-state, may serve as a\nstarting point in the experimental study of the nonlinear tunneling in the 3D\nlattice.", "category": "cond-mat_other" }, { "text": "Evolution of a quantum spin system to its ground state: Role of\n entanglement and interaction symmetry: We study the decoherence of two ferro- and antiferromagnetically coupled\nspins that interact with a frustrated spin-bath environment in its ground\nstate. The conditions under which the two-spin system relaxes from the initial\nspin-up - spin-down state towards its ground state are determined. It is shown\nthat the two-spin system relaxes to its ground state for narrow ranges of the\nmodel parameters only. It is demonstrated that the symmetry of the coupling\nbetween the two-spin system and the environment has an important effect on the\nrelaxation process. In particular, we show that if this coupling conserves the\nmagnetization, the two-spin system readily relaxes to its ground state whereas\na non-conserving coupling prevents the two-spin system from coming close to its\nground state.", "category": "cond-mat_other" }, { "text": "Comment on \"Fully covariant radiation force on a polarizable particle\": Recently Pieplow and Henkel (PH) (NJP \\textbf{15} (2013) 023027) presented a\nnew fully covariant theory of the Casimir friction force acting on small\nneutral particle moving parallel to flat surface. We compare results of this\ntheory with results which follow from a fully relativistic theory of friction\nin plate-plate configurations in the limit when one plate is considered as\nsufficiently rarefied. We show that there is the agreement between these\ntheories.", "category": "cond-mat_other" }, { "text": "Conditions for the Existence of Polaron States in Classical Molecular\n Chains at Finite Temperatures: Today in many articles the polaron states are calculated in classical\nmolecular chains for zero temperature. At the same time it is assumed that\npolaron properties do not change significantly, if the temperature is nonzero,\nbut much smaller than the characteristic energy equal to the depth of the\npolaron level. However, the results of computational experiments lead us to\nsuggestion that in infinitely long chain the polaron is destroyed at any small\ndifferent from zero temperature. The paper is devoted to the resolution of\ndescribed \"paradoxical\" situation.", "category": "cond-mat_other" }, { "text": "Complex Envelope Soliton in Bose-Einstein Condensate with Time Dependent\n Scattering Length: We elaborate on a general method to find complex envelope solitons in a cigar\nshaped Bose-Einstein condensate in a trap. The procedure incorporates time\ndependent scattering length, oscillator frequency and loss/gain. A variety of\ntime dependencies of the above parameters, akin to the ones occurring in the\nexperiments can be tackled.", "category": "cond-mat_other" }, { "text": "Importance of bath dynamics for decoherence in spin systems: We study the decoherence of two coupled spins that interact with a chaotic\nspin-bath environment. It is shown that connectivity of spins in the bath is of\ncrucial importance for the decoherence of the central system. The previously\nfound phenomenon of two-step decoherence (Phys. Rev. Lett. {\\bf 90}, 210401\n(2003)) turns out to be typical for the bath with a slow enough dynamics or no\ndynamics. For a generic random system with chaotic dynamics a conventional\nexponential relaxation to the pointer states takes place. Our results confirm a\nconjecture of Paz and Zurek (Phys. Rev. Lett. {\\bf 82}, 5181 (1999)) that for\nweak enough interactions the pointer states are eigenstates of the central\nsystem.", "category": "cond-mat_other" }, { "text": "Self-induced density modulations in the free expansion of Bose-Einstein\n condensates: We simulate numerically the free expansion of a repulsive Bose-Einstein\ncondensate with an initially Gaussian density profile. We find a self-similar\nexpansion only for weak inter-atomic repulsion. In contrast, for strong\nrepulsion we observe the spontaneous formation of a shock wave at the surface\nfollowed by a significant depletion inside the cloud. In the expansion,\ncontrary to the case of a classical viscous gas, the quantum fluid can generate\nradial rarefaction density waves with several minima and maxima. These\nintriguing nonlinear effects, never observed yet in free-expansion experiments\nwith ultra-cold alkali-metal atoms, can be detected with the available setups.", "category": "cond-mat_other" }, { "text": "Continuum Mechanics for Quantum Many-Body Systems: The Linear Response\n Regime: We derive a closed equation of motion for the current density of an\ninhomogeneous quantum many-body system under the assumption that the\ntime-dependent wave function can be described as a geometric deformation of the\nground-state wave function. By describing the many-body system in terms of a\nsingle collective field we provide an alternative to traditional approaches,\nwhich emphasize one-particle orbitals. We refer to our approach as continuum\nmechanics for quantum many-body systems. In the linear response regime, the\nequation of motion for the displacement field becomes a linear fourth-order\nintegro-differential equation, whose only inputs are the one-particle density\nmatrix and the pair correlation function of the ground-state. The complexity of\nthis equation remains essentially unchanged as the number of particles\nincreases. We show that our equation of motion is a hermitian eigenvalue\nproblem, which admits a complete set of orthonormal eigenfunctions under a\nscalar product that involves the ground-state density. Further, we show that\nthe excitation energies derived from this approach satisfy a sum rule which\nguarantees the exactness of the integrated spectral strength. Our formulation\nbecomes exact for systems consisting of a single particle, and for any\nmany-body system in the high-frequency limit. The theory is illustrated by\nexplicit calculations for simple one- and two-particle systems.", "category": "cond-mat_other" }, { "text": "Comment on \"Amplitude of waves in the Kelvin-wave cascade\": In the recently published preprint arXiv:200.02610 Eltsov and L'vov\ncalculated the amplitudes of waves in the Kelvin-wave cascades. This returns us\nto the rather old, but still unresolved dispute on the role of the tilt\nsymmetry and the locality in the Kelvin-wave cascade. The estimations by Eltsov\nand L'vov show that the possible nonlocality of the energy flux in the\nKelvin-wave cascade has no essential effect on the Kelvin-wave cascade in the\n3D vortex tangle.", "category": "cond-mat_other" }, { "text": "Spin-transfer mechanism of ferromagnetism in polymerized fullerenes: $Ab\n initio$ calculations: A mechanism of the high temperature ferromagnetism in polymerized fullerenes\nis suggested. It is assumed that some of the C$_{60}$ molecules in the crystal\nbecome magnetically active due to spin and charge transfer from the\nparamagnetic impurities (atoms or groups), such as hydrogen, fluorine, hydroxyl\ngroup OH, amino group NH$_2$, or methyl group CH$_3$, dispersed in the\nfullerene matrix. The exchange interaction between the spins localized on the\nmagnetically active fullerenes is evaluated using \\textit{ab initio}\ncalculations. The nearest neighbour and next nearest neighbour exchange\ninteraction is found to be in the range $0.1\\div 0.3 $ eV, that is, high enough\nto account for the room temperature ferromagnetism.", "category": "cond-mat_other" }, { "text": "A Quantum Top Inside a Bose Josephson Junction: We consider an atomic quantum dot confined between two weakly-coupled\nBose-Einstein condensates, where the dot serves as an additional tunneling\nchannel. It is shown that the thus-embedded atomic quantum dot is a pseudospin\nsubject to an external torque, and therefore equivalent to a quantum top. We\ndemonstrate by numerical analysis of the time-dependent coupled evolution\nequations that this microscopic quantum top is very sensitive to any deviation\nfrom linear oscillatory behavior of the condensates. For sufficiently strong\ndot-condensate coupling, the atomic quantum dot can induce or modify the\ntunneling between the macroscopic condensates in the two wells.", "category": "cond-mat_other" }, { "text": "Dark state experiments with ultracold, deeply-bound triplet molecules: We examine dark quantum superposition states of weakly bound Rb2 Feshbach\nmolecules and tightly bound triplet Rb2 molecules in the rovibrational ground\nstate, created by subjecting a pure sample of Feshbach molecules in an optical\nlattice to a bichromatic Raman laser field. We analyze both experimentally and\ntheoretically the creation and dynamics of these dark states. Coherent\nwavepacket oscillations of deeply bound molecules in lattice sites, as observed\nin one of our previous experiments, are suppressed due to laser-induced phase\nlocking of molecular levels. This can be understood as the appearance of a\nnovel multilevel dark state. In addition, the experimental methods developed\nhelp to determine important properties of our coupled atom / laser system.", "category": "cond-mat_other" }, { "text": "Ground State and Tkachenko Modes of a Rapidly Rotating Bose-Einstein\n Condensate in the Lowest Landau Level State: The Letter considers the ground state and the Tkachenko modes for a rapidly\nrotating Bose-Einstein condensate (BEC), when its macroscopic wave function is\na coherent superposition of states analogous to the lowest Landau levels of a\ncharge in a magnetic field. As well as in type II superconductors close to the\ncritical magnetic field $H_{c2}$, this corresponds to a periodic vortex\nlattice. The exact value of the shear elastic modulus of the vortex lattice,\nwhich was known from the old works on type II superconductors, essentially\nexceeds the values calculated recently for BEC. This is important for\ncomparison with observation of the Tkachenko mode in the rapidly rotating BEC.", "category": "cond-mat_other" }, { "text": "A Twisted Pair Cryogenic Filter: In low temperature transport measurements, there is frequently a need to\nprotect a device at cryogenic temperatures from thermal noise originating in\nwarmer parts of the experiment. There are also a wide range of experiments,\nsuch as high precision transport measurements on low impedance devices, in\nwhich a twisted-pair wiring configuration is useful to eliminate magnetic\npickup. Furthermore, with the rapid growth in complexity of cryogenic\nexperiments, as in the field of quantum computing, there is a need for more\nfiltered lines into a cryostat than are often available using the bulky low\ntemperature filters in use today. We describe a low cost filter that provides\nthe needed RF attenuation while allowing for tens of wires in a twisted pair\nconfiguration with an RF-tight connection to the sample holder. Our filter\nconsists of manganin twisted pairs wrapped in copper tape with a light-tight\nconnection to the shield of the sample holder. We demonstrate agreement of our\nfilter with a theoretical model up to the noise floor of our measurement\napparatus (90 dB). We describe operation of our filter in noise thermometry\nexperiments down to 10 mK.", "category": "cond-mat_other" }, { "text": "The Moment Map: Nonlinear dynamics of density evolution via a few\n moments: We explore situations in which certain stochastic and high-dimensional\ndeterministic systems behave effectively as low-dimensional dynamical systems.\nWe define and study moment maps, maps on spaces of low-order moments of\nevolving distributions, as a means of understanding equations-free multiscale\nalgorithms for these systems. We demonstrate how nonlinearity arises in these\nmaps and how this results in the stabilization of metastable states. Examples\nare shown for a hierarchy of models, ranging from simple stochastic\ndifferential equations to molecular dynamics simulations of a particle in\ncontact with a heat bath.", "category": "cond-mat_other" }, { "text": "Optical properties of atomic Mott insulators: from slow light to\n dynamical Casimir effects: We theoretically study the optical properties of a gas of ultracold,\ncoherently dressed three-level atoms in a Mott insulator phase of an optical\nlattice. The vacuum state, the band dispersion and the absorption spectrum of\nthe polariton field can be controlled in real time by varying the amplitude and\nthe frequency of the dressing beam. In the weak dressing regime, the system\nshows unique ultra-slow light propagation properties without absorption. In the\npresence of a fast time modulation of the dressing amplitude, we predict a\nsignificant emission of photon pairs by parametric amplification of the\npolaritonic zero-point fluctuations. Quantitative considerations on the\nexperimental observability of such a dynamical Casimir effect are presented for\nthe most promising atomic species and level schemes.", "category": "cond-mat_other" }, { "text": "Intrinsic relation between ground-state fidelity and the\n characterization of a quantum phase transition: The notion of fidelity in quantum information science has been recently\napplied to analyze quantum phase transitions from the viewpoint of the ground\nstate (GS) overlap for various many-body systems. In this work, we unveil the\nintrinsic relation between the GS fidelity and the derivatives of GS energy and\nfind that they play equivalent role in identifying the quantum phase\ntransition. The general connection between the two approaches enables us to\nunderstand the different singularity and scaling behaviors of fidelity\nexhibited in various systems on general grounds. Our general conclusions are\nillustrated via several quantum spin models which exhibit different kinds of\nQPTs.", "category": "cond-mat_other" }, { "text": "Coherent electronic transfer in quantum dot systems using adiabatic\n passage: We describe a scheme for using an all-electrical, rapid, adiabatic population\ntransfer between two spatially separated dots in a triple-quantum dot system.\nThe electron spends no time in the middle dot and does not change its energy\nduring the transfer process. Although a coherent population transfer method,\nthis scheme may well prove useful in incoherent electronic computation (for\nexample quantum-dot cellular automata) where it may provide a coherent\nadvantage to an otherwise incoherent device. It can also be thought of as a\nlimiting case of type II quantum computing, where sufficient coherence exists\nfor a single gate operation, but not for the preservation of superpositions\nafter the operation. We extend our analysis to the case of many intervening\ndots and address the issue of transporting quantum information through a\nmulti-dot system.", "category": "cond-mat_other" }, { "text": "Molecular-dynamics simulation of clustering processes in sea-ice floes: In seasonally ice-covered seas and along the margins of perennial ice pack,\ni.e. in regions with medium ice concentrations, the ice cover typically\nconsists of separate floes interacting with each other by inelastic collisions.\nIn this paper, hitherto unexplored analogies between this type of ice cover and\ntwo-dimensional granular gases are used to formulate a model of ice dynamics at\nthe floe level. The model consists of: (i) momentum equations for floe motion\nbetween collisions, formulated in the form of a Stokes-flow problem, with\nfloe-size dependent time constant and equilibrium velocity, and (ii) hard-disk\ncollision model. The numerical algorithm developed is suitable for simulating\nparticle-laden flow of $N$ disk-shaped floes with arbitrary size distribution.\nThe model is applied to study clustering phenomena in sea ice with power-law\nfloe-size distribution. In particular, the influence of the average ice\nconcentration $\\bar{A}$ on the formation and characteristics of clusters is\nanalyzed in detail. The results show the existence of two regimes, at low and\nhigh ice concentration, differing in terms of the exponents of the cluster-size\ndistribution and of the size of the largest cluster.", "category": "cond-mat_other" }, { "text": "Two roads to antispacetime in polar distorted B phase: Kibble wall and\n half-quantum vortex: We consider the emergent tetrad gravity and the analog of antispacetime\nrealized in the recent experiments ( J.T. Makinen, et al., Nat. Comm. 10, 237\n(2019)) on the composite defects in superfluid $^3$He: the Kibble walls bounded\nby strings (the half quantum vortices). The antispacetime can be reached in two\ndifferent ways: by the \"safe\" route around the Alice string or by dangerous\nroute across the Kibble wall. This consideration also suggests the scenario of\nthe formation of the discrete symmetry -- the parity $P$ in Dirac equations --\nfrom the continuous symmetry existing on the more fundamental level.", "category": "cond-mat_other" }, { "text": "Collisions between tunable halo dimers: exploring an elementary\n four-body process with identical bosons: We study inelastic collisions in a pure, trapped sample of Feshbach molecules\nmade of bosonic cesium atoms in the quantum halo regime. We measure the\nrelaxation rate coefficient for decay to lower-lying molecular states and study\nthe dependence on scattering length and temperature. We identify a pronounced\nloss minimum with varying scattering length along with a further suppression of\nloss with decreasing temperature. Our observations provide insight into the\nphysics of a few-body quantum system that consists of four identical bosons at\nlarge values of the two-body scattering length.", "category": "cond-mat_other" }, { "text": "Single-atom doping for quantum device development in diamond and silicon: The ability to inject dopant atoms with high spatial resolution, flexibility\nin dopant species and high single ion detection fidelity opens opportunities\nfor the study of dopant fluctuation effects and the development of devices in\nwhich function is based on the manipulation of quantum states in single atoms,\nsuch as proposed quantum computers. We describe a single atom injector, in\nwhich the imaging and alignment capabilities of a scanning force microscope\n(SFM) are integrated with ion beams from a series of ion sources and with\nsensitive detection of current transients induced by incident ions. Ion beams\nare collimated by a small hole in the SFM tip and current changes induced by\nsingle ion impacts in transistor channels enable reliable detection of single\nion hits. We discuss resolution limiting factors in ion placement and\nprocessing and paths to single atom (and color center) array formation for\nsystematic testing of quantum computer architectures in silicon and diamond.", "category": "cond-mat_other" }, { "text": "Energy concentration in composite quantum systems: The spontaneous emission of photons from optical cavities and from trapped\natoms has been studied extensively in the framework of quantum optics.\nTheoretical predictions based on the rotating wave approximation (RWA) are in\ngeneral in very good agreement with experimental findings. However, current\nexperiments aim at combining better and better cavities with large numbers of\ntightly confined atoms. Here we predict an energy concentrating mechanism in\nthe behavior of such a composite quantum system which cannot be described by\nthe RWA. Its result is the continuous leakage of photons through the cavity\nmirrors, even in the absence of external driving. We conclude with a discussion\nof the predicted phenomenon in the context of thermodynamics.", "category": "cond-mat_other" }, { "text": "A controllable nanomechanical memory element: We report the realization of a completely controllable high-speed\nnanomechanical memory element fabricated from single-crystal silicon wafers.\nThis element consists of a doubly-clamped suspended nanomechanical beam\nstructure, which can be made to switch controllably between two stable and\ndistinct states at a single frequency in the megahertz range. Because of their\nsub-micron size and high normal-mode frequencies, these nanomechanical memory\nelements offer the potential to rival the current state-of-the-art electronic\ndata storage and processing.", "category": "cond-mat_other" }, { "text": "On the Transition to Turbulence of Oscillatory Flow of Liquid Helium-4: Oscillating solid bodies have frequently been used for studying the\nproperties of normal and superfluid helium. In particular, the transition from\nlaminar flow to turbulence has attracted much interest recently. The purpose of\nthis note is to review several central features of this transition in\noscillatory flow, which have been inaccurately formulated in some recent work.", "category": "cond-mat_other" }, { "text": "Motional Averaging of Nuclear Resonance in a Field Gradient: The traditional view of nuclear-spin decoherence in a field gradient due to\nmolecular self-diffusion is challenged on the basis of temperature dependence\nof the linewidth, which demonstrates different behaviors between liquids and\ngases. The conventional theory predicts that in a fluid, linewidth should\nincrease with temperature; however, in gases we observed the opposite behavior.\nThis surprising behavior can be explained using a more detailed theoretical\ndescription of the dephasing function that accounts for position\nautocorrelation effects.", "category": "cond-mat_other" }, { "text": "Electron dynamics in vacancy islands: The dynamics of Ag(111) surface state electrons confined to nanoscale\nhexagonal and triangular vacancy islands are investigated using scanning\ntunneling spectroscopy. The lifetimes of quantised states with significant\namplitude near the centers of the vacancies are weakly affected by the geometry\nof the confining cavity. A model that includes the dependence of the lifetime\non electron energy, vacancy size, step reflectivity and the phase coherence\nlength describes the results well. For vacancy islands with areas in the range\n$\\approx 40$--$220 {\\rm nm}^2$ lossy scattering is the dominant\nlifetime-limiting process. This result and a corrected analysis of published\nexperimental data improve the consistency of experimental and calculated\nsurface state lifetimes.", "category": "cond-mat_other" }, { "text": "Current-induced interactions of multiple domain walls in magnetic\n quantum wires: We show that an applied charge current in a magnetic nanowire containing\ndomain walls (DWs) results in an interaction between DWs mediated by\nspin-dependent interferences of the scattered carriers. The energy and torque\nassociated with this interaction show an oscillatory behaviour as a function of\nthe mutual DWs orientations and separations, thus affecting the DWs'\narrangements and shapes. Based on the derived DWs interaction energy and torque\nwe calculate DW dynamics and uncover potential applications of interacting DWs\nas a tunable nano-mechanical oscillator. We also discuss the effect of\nimpurities on the DW interaction.", "category": "cond-mat_other" }, { "text": "Natural Negative-Refractive-Index Materials: Our calculation shows that negative refractive index (NRI), which was known\nto exist only in metamaterials in the past, can be found in Dirac semimetals\n(DSM). Electrons in DSM have zero effective mass and hence the system carries\nno nominal energy scale. Therefore, unlike those of ordinary materials, the\nelectromagnetic responses of the electrons in DSM will not be overwhelmed by\nthe physical effects related to electron mass. NRI is induced by the\ncombination of the quantum effect of vacuum polarization and its finite\ntemperature correction which is proportional to $T^4$ at low temperature. It is\na phenomenon of resonance between the incident light and the unique structure\nof Dirac cones, which allows numerous states to participate in electron-hole\npair production excited by the incident light with similar dispersion relation\nto that of Dirac cones. NRI phenomenon of DSM manifests in an extensive range\nof photon frequency and wave number and can be observed around giga Hertz range\nat temperature slightly higher than room temperature.", "category": "cond-mat_other" }, { "text": "An Investigation of Mean-field Effects for a Bose Condensate in an\n Optical Lattice: This paper presents a mean-field numerical analysis, using the full\nthree-dimensional time-dependent Gross-Pitaevskii equation (GPE), of an\nexperiment carried out by Orzel et al. [Science 291, 2386 (2001)] intended to\nshow number squeezing in a gaseous Bose-Einstein condensate in an optical\nlattice. The motivation for the present work is to elucidate the role of\nmean-field effects in understanding the experimental results of this work and\nthose of related experiments. We show that the non-adiabatic loading of atoms\ninto optical lattices reproduces many of the main results of the Orzel et al.\nexperiment, including both loss of interference patterns as laser intensity is\nincreased and their regeneration when intensities are lowered. The\nnon-adiabaticity found in the GPE simulations manifests itself primarily in a\ncoupling between the transverse and longitudinal dynamics, indicating that\none-dimensional approximations are inadequate to model the experiment.", "category": "cond-mat_other" }, { "text": "The free surface of superfluid 4He at zero temperature: The structure and energetics of the free surface of superfluid $^4$He are\nstudied using the diffusion Monte Carlo method. Extending a previous\ncalculation by Vall\\'es and Schmidt, which used the Green's function Monte\nCarlo method, we study the surface of liquid $^4$He within a slab geometry\nusing a larger number of particles in the slab and an updated interatomic\npotential. The surface tension is accurately estimated from the energy of slabs\nof increasing surface density and its value is close to one of the two existing\nexperimental values. Results for the density profiles allow for the calculation\nof the surface width which shows an overall agreement with recent experimental\ndata. The dependence on the transverse direction to the surface of other\nproperties such as the two-body radial distribution function, structure factor,\nand one-body density matrix is also studied. The condensate fraction, extracted\nfrom the asymptotic behavior of the one-body density matrix, shows an\nunambiguous enhancement when approaching the surface.", "category": "cond-mat_other" }, { "text": "Topological Constraints on the Charge Distributions for the Thomson\n Problem: The method of Morse theory is used to analyze the distributions of unit\ncharges interacting through a repulsive force and constrained to move on the\nsurface of a sphere -- the Thomson problem. We find that, due to topological\nreasons, the system may organize itself in the form of pentagonal structures.\nThis gives a qualitative account for the interesting ``pentagonal buttons''\ndiscovered in recent numerical work.", "category": "cond-mat_other" }, { "text": "Measuring the spin polarization and Zeeman energy of a spin-polarized\n electron gas: Comparison between Raman scattering and photoluminescence: We compare resonant electronic Raman scattering and photoluminescence\nmeasurements for the characterization of a spin-polarized two-dimensional\nelectron gas embedded in $\\text{Cd}_{1-x}\\text{Mn}_x\\text{Te}$ single quantum\nwells. From Raman scattering by single-particle excitations in a zero magnetic\nfield, we measure the Fermi velocity and then obtain the Fermi energy (as well\nas the electron density), which is comparable to that extracted from\nphotoluminescence for moderate electron densities, assuming a bare band-edge\nmass. At large electron densities, the Fermi energies derived from Raman\nscattering and photoluminescence differ. For an applied in-plane magnetic field\nand zero wave vector transferred to the electron gas, Raman scattering spectra\nshow peaks at both the Zeeman energy $Z$, resulting from collective excitations\nof the spin-polarized electron gas, and the one electron spin-flip energy\n$Z^*$. Magneto-photoluminescence spectra show conduction band splitting that\nare equivalent to $Z$, suggesting that collective effects are present in the\nphotoluminescence spectra. Assuming (as before) an uncorrected mass, the degree\nof spin polarization $\\zeta$ determined from the magneto-photoluminescence\nlineshape is found to differ from that derived from the magnetic field\ndependent Raman scattering measurements for large electron densities. We\nattribute the discrepancy in measuring $\\zeta$ and the Fermi energy to the\nrenormalized mass resulting from many-body electron-electron interactions.", "category": "cond-mat_other" }, { "text": "Bipartite Yule Processes in Collections of Journal Papers: Collections of journal papers, often referred to as 'citation networks', can\nbe modeled as a collection of coupled bipartite networks which tend to exhibit\nlinear growth and preferential attachment as papers are added to the\ncollection. Assuming primary nodes in the first partition and secondary nodes\nin the second partition, the basic bipartite Yule process assumes that as each\nprimary node is added to the network, it links to multiple secondary nodes, and\nwith probability, $\\alpha$, each new link may connect to a newly appearing\nsecondary node. The number of links from a new primary node follows some\ndistribution that is a characteristic of the specific network. Links to\nexisting secondary nodes follow a preferential attachment rule. With\nmodifications to adapt to specific networks, bipartite Yule processes simulate\nnetworks that can be validated against actual networks using a wide variety of\nnetwork metrics. The application of bipartite Yule processes to the simulation\nof paper-reference networks and paper-author networks is demonstrated and\nsimulation results are shown to mimic networks from actual collections of\npapers across several network metrics.", "category": "cond-mat_other" }, { "text": "Quantum fluid effects and parametric instabilities in microcavities: We present a description of the non-equilibrium properties of a microcavity\npolariton fluid, injected by a nearly-resonant continuous wave pump laser. In\nthe first part, we point out the interplay between the peculiar dispersion of\nthe Bogolubov-like polariton excitations and the onset of polariton parametric\ninstabilities. We show how collective excitation spectra having no counterpart\nin equilibrium systems can be observed by tuning the excitation angle and\nfrequency. In the second part, we explain the impact of these collective\nexcitations on the in-plane propagation of the polariton fluid. We show that\nthe resonant Rayleigh scattering induced by artificial or natural defects is a\nvery sensitive tool to show fascinating effects such as polariton superfluidity\nor polariton Cherenkov effect. We present a comprehensive set of predicted\nfar-field and near-field images for the resonant Rayleigh scattering emission.", "category": "cond-mat_other" }, { "text": "Transport and recombination through weakly coupled localized spin pairs\n in semiconductors during coherent spin excitation: Semi-analytical predictions for the transients of spin-dependent transport\nand recombination rates through localized states in semiconductors during\ncoherent electron spin excitation are made for the case of weakly spin-coupled\ncharge carrier ensembles. The results show that the on-resonant Rabi frequency\nof electrically or optically detected spin-oscillation doubles abruptly as the\nstrength of the resonant microwave field gamma B_1 exceeds the Larmor frequency\nseparation within the pair of charge carrier states between which the transport\nor recombination transition takes place. For the case of a Larmor frequency\nseparation of the order of gamma B_1 and arbitrary excitation frequencies, the\ncharge carrier pairs exhibit four different nutation frequencies. From the\ncalculations, a simple set of equations for the prediction of these frequencies\nis derived.", "category": "cond-mat_other" }, { "text": "Quantum Monte Carlo study of ring-shaped polariton parametric\n luminescence in a semiconductor microcavity: We present a quantum Monte Carlo study of the quantum correlations in the\nparametric luminescence from semiconductor microcavities in the strong\nexciton-photon coupling regime. As already demonstrated in recent experiments,\na ring-shaped emission is obtained by applying two identical pump beams with\nopposite in-plane wavevectors, providing symmetrical signal and idler beams\nwith opposite in-plane wavevectors on the ring. We study the squeezing of the\nsignal-idler difference noise across the parametric instability threshold,\naccounting for the radiative and non-radiative losses, multiple scattering and\nstatic disorder. We compare the results of the complete multimode Monte Carlo\nsimulations with a simplified linearized quantum Langevin analytical model.", "category": "cond-mat_other" }, { "text": "Effect of interactions on the localization of a Bose-Einstein condensate\n in a quasi-periodic lattice: The transport properties of a Bose-Einstein condensate in a 1D incommensurate\nbichromatic lattice are investigated both theoretically and experimentally. We\nobserve a blockage of the center of mass motion with low atom number, and a\nreturn of motion when the atom number is increased. Solutions of the\nGross-Pitaevskii equation show how the localization due to the quasi-disorder\nintroduced by the incommensurate bichromatic lattice is affected by the\ninteractions.", "category": "cond-mat_other" }, { "text": "Alignment of the Diamond Nitrogen Vacancy Center by Strain Engineering: The nitrogen vacancy (NV) center in diamond is a sensitive probe of magnetic\nfield and a promising qubit candidate for quantum information processing. The\nperformance of many NV-based devices improves by aligning the NV(s) parallel to\na single crystallographic direction. Using ab initio theoretical techniques, we\nshow that NV orientation can be controlled by high-temperature annealing in the\npresence of strain under currently accessible experimental conditions. We find\nthat $(89\\pm7)\\%$ of NVs align along the [111] crystallographic direction under\n2\\% compressive biaxial strain (perpendicular to [111]) and an annealing\ntemperature of 970$^\\circ$C.", "category": "cond-mat_other" }, { "text": "Current-induced spin torques in III-V ferromagnetic semiconductors: We formulate a theory of current-induced spin torques in inhomogeneous III-V\nferromagnetic semiconductors. The carrier spin-3/2 and large spin-orbit\ninteraction, leading to spin non-conservation, introduce significant conceptual\ndifferences from spin torques in ferromagnetic metals. We determine the spin\ndensity in an electric field in the weak momentum scattering regime,\ndemonstrating that the torque on the magnetization is intimately related to\nspin precession under the action of both the spin-orbit interaction and the\nexchange field characteristic of ferromagnetism. The spin polarization excited\nby the electric field is smaller than in ferromagnetic metals and, due to lack\nof angular momentum conservation, cannot be expressed in a simple closed\nvectorial form. Remarkably, scalar and spin-dependent scattering do not affect\nthe result. We use our results to estimate the velocity of current-driven\ndomain walls.", "category": "cond-mat_other" }, { "text": "Electron inelastic mean free paths in condensed matter down to a few\n electronvolts: A method is reported for a simple, yet reliable, calculation of electron\ninelastic mean free paths in condensed phase insulating and conducting\nmaterials, from the very low energies of hot electrons up to the high energies\ncharacteristic of electron beams. Through a detailed consideration of the\nenergy transferred by the projectile in individual and collective electronic\nexcitations, as well as ionizations, together with the inclusion of higher\norder corrections to the results provided by the dielectric formalism,\ninelastic mean free paths are calculated for water, aluminum, gold and copper\nin excellent agreement with the available experimental data, even at the\nelusive very low energy region. These results are important due to the crucial\nrole played by low energy electrons in radiobiology (owing to their relevant\neffects in biodamage), and also in order to assess the not yet elucidated\ndisagreement between older and recent measurements of low energy electron mean\nfree paths in metals (which are relevant for low energy electron transport and\neffects in nanostructured devices).", "category": "cond-mat_other" }, { "text": "Numerical Study on Entrance Length in Thermal Counterflow of Superfluid\n $^4$He: Three-dimensional numerical simulations in a square duct were conducted to\ninvestigate entrance lengths of normal fluid and superfluid flows in a thermal\ncounterflow of superfluid $^4$He. The two fluids were coarse-grained by using\nthe Hall-Vinen-Bekharevich-Khalatnikov (HVBK) model and were coupled through\nmutual friction. We solved the HVBK equations by parameterizing the coefficient\nof the mutual friction to consider the vortex line density. A uniform mutual\nfriction parameter was assumed in the streamwise direction. Our simulation\nshowed that the entrance length of the normal fluid from a hot end becomes\nshorter than that of a single normal fluid due to the mutual friction with the\nparabolically developed superfluid flow near the hot end. As the mutual\nfriction increases, the entrance length decreases. Same as that, the entrance\nlength of the superfluid from a cold end is affected by the strength of the\nmutual friction due to the parabolically developed normal fluid flow near the\ncold end. Aside from the entrance effect, the realized condition of a\ntail-flattened flow is discussed by parameterizing the superfluid turbulent\neddy viscosity and the mutual friction.", "category": "cond-mat_other" }, { "text": "Many-body perturbation theory using the density-functional concept:\n beyond the GW approximation: We propose an alternative formulation of Many-Body Perturbation Theory that\nuses the density-functional concept. Instead of the usual four-point integral\nequation for the polarizability, we obtain a two-point one, that leads to\nexcellent optical absorption and energy loss spectra. The corresponding\nthree-point vertex function and self-energy are then simply calculated via an\nintegration, for any level of approximation. Moreover, we show the direct\nimpact of this formulation on the time-dependent density-functional theory.\nNumerical results for the band gap of bulk silicon and solid argon illustrate\ncorrections beyond the GW approximation for the self-energy.", "category": "cond-mat_other" }, { "text": "Influence of the substrate lattice structure on the formation of Quantum\n Well States in thin In and Pb films on silicon: The substrate lattice structure may have a considerable influence on the\nformation of quantum well states in a metal overlayer material. Here we study\nthree model systems using angle resolved photoemission and low energy electron\ndiffraction: indium films on Si(111) and indium and lead on Si(100). Data are\ncompared with theoretical predictions based on density functional theory. We\nfind that the interaction between the substrate and the overlayer strongly\ninfluences the formation of quantum well states; indium layers only exhibit\nwell defined quantum well states when the layer relaxes from an initial\nface-centered cubic to the bulk body-centered tetragonal lattice structure. For\nPb layers on Si(100) a change in growth orientation inhibits the formations of\nquantum well states in films thicker than 2 ML.", "category": "cond-mat_other" }, { "text": "Supersolids in one dimensional Bose Fermi mixtures: Using quantum Monte Carlo simulations, we study a mixture of bosons and\nfermions loaded on an optical lattice. With simple on-site repulsive\ninteractions, this system can be driven into a solid phase. We dope this phase\nand, in analogy with pure bosonic systems, identify the conditions under which\nthe bosons enter a supersolid phase, i.e., exhibiting at the same time charge\ndensity wave and superfluid order. We perform finite size scaling analysis to\nconfirm the presence of a supersolid phase and discuss its properties, showing\nthat it is a collective phase that also involve phase coherence of the\nfermions.", "category": "cond-mat_other" }, { "text": "Observation of Majorana Quasiparticles Surface States in Superfluid\n ${^3}$He-B by Heat Capacity Measurements: We report about direct measurements of heat capacity of Majorana\nquasiparticles in superfluid ${^3}$He-B which appear near the surface of the\nexperimental bolometer on the coherence length ${\\xi}$. Two bolometers with\ndifferent surface-to-volume ratios were used which allows us to have different\ncalibrated contributions from Majorana quasiparticles to the ${^3}$He heat\ncapacity. Estimations of possible impact of ${^3}$He layers adsorbed on the\nwalls of the bolometer have been done.", "category": "cond-mat_other" }, { "text": "Electron effective mobility in strained Si/Si1-xGex MOS devices using\n Monte Carlo simulation: Based on Monte Carlo simulation, we report the study of the inversion layer\nmobility in n-channel strained Si/ Si1-xGex MOS structures. The influence of\nthe strain in the Si layer and of the doping level is studied. Universal\nmobility curves mueff as a function of the effective vertical field Eeff are\nobtained for various state of strain, as well as a fall-off of the mobility in\nweak inversion regime, which reproduces correctly the experimental trends. We\nalso observe a mobility enhancement up to 120 % for strained Si/ Si0.70Ge0.30,\nin accordance with best experimental data. The effect of the strained Si\nchannel thickness is also investigated: when decreasing the thickness, a\nmobility degradation is observed under low effective field only. The role of\nthe different scattering mechanisms involved in the strained Si/ Si1-xGex MOS\nstructures is explained. In addition, comparison with experimental results is\ndiscussed in terms of SiO2/ Si interface roughness, as well as surface\nroughness of the SiGe substrate on which strained Si is grown.", "category": "cond-mat_other" }, { "text": "Adiabatic and Non-Adiabatic Contributions to the Free Energy from the\n Electron-Phonon Interaction for Na, K, Al, and Pb: We calculate the adiabatic contributions to the free energy due to the\nelectron--phonon interaction at intermediate temperatures, $0 \\leqslant k_{B} T\n< \\epsilon_{F}$ for the elemental metals Na, K, Al, and Pb. Using our\npreviously published results for the nonadiabatic contributions we show that\nthe adiabatic contribution, which is proportional to $T^{2}$ at low\ntemperatures and goes as $T^{3}$ at high temperatures, dominates the\nnonadiabatic contribution for temperatures above a cross--over temperature,\n$T_{c}$, which is between 0.5 and 0.8 $T_{m}$, where $T_{m}$ is the melting\ntemperature of the metal. The nonadiabatic contribution falls as $T^{-1}$ for\ntemperatures roughly above the average phonon frequency.", "category": "cond-mat_other" }, { "text": "Superradiant scattering from a hydrodynamic vortex: We show that sound waves scattered from a hydrodynamic vortex may be\namplified. Such superradiant scattering follows from the physical analogy\nbetween spinning black holes and hydrodynamic vortices. However a sonic horizon\nanalogous to the black hole event horizon does not exist unless the vortex\npossesses a central drain, which is challenging to produce experimentally. In\nthe astrophysical domain, superradiance can occur even in the absence of an\nevent horizon: we show that in the hydrodynamic analogue, a drain is not\nrequired and a vortex scatters sound superradiantly. Possible experimental\nrealization in dilute gas Bose-Einstein condensates is discussed.", "category": "cond-mat_other" }, { "text": "The angular momentum of a magnetically trapped atomic condensate: For an atomic condensate in an axially symmetric magnetic trap, the sum of\nthe axial components of the orbital angular momentum and the hyperfine spin is\nconserved. Inside an Ioffe-Pritchard trap (IPT) whose magnetic field (B-field)\nis not axially symmetric, the difference of the two becomes surprisingly\nconserved. In this paper we investigate the relationship between the values of\nthe sum/difference angular momentums for an atomic condensate inside a magnetic\ntrap and the associated gauge potential induced by the adiabatic approximation.\nOur result provides significant new insight into the vorticity of magnetically\ntrapped atomic quantum gases.", "category": "cond-mat_other" }, { "text": "Equation of state of cubic boron nitride at high pressures and\n temperatures: We report accurate measurements of the equation of state (EOS) of cubic boron\nnitride by x-ray diffraction up to 160 GPa at 295 K and 80 GPa in the range\n500-900 K. Experiments were performed on single-crystals embedded in a\nquasi-hydrostatic pressure medium (helium or neon). Comparison between the\npresent EOS data at 295 K and literature allows us to critically review the\nrecent calibrations of the ruby standard. The full P-V-T data set can be\nrepresented by a Mie-Gr\\\"{u}neisen model, which enables us to extract all\nrelevant thermodynamic parameters: bulk modulus and its first\npressure-derivative, thermal expansion coefficient, thermal Gr\\\"{u}neisen\nparameter and its volume dependence. This equation of state is used to\ndetermine the isothermal Gr\\\"{u}neisen mode parameter of the Raman TO band. A\nnew formulation of the pressure scale based on this Raman mode, using\nphysically-constrained parameters, is deduced.", "category": "cond-mat_other" }, { "text": "Remarks on the lattice Green's Function for the anisotropic Face\n Centered Cubic Lattice: An expression for the Green's function (GF) of anisotropic face centered\ncubic lattice is evaluated analytically and numerically for a single impurity\nproblem. The density of states (DOS), phase shift and scattering cross section\nare expressed in terms of complete elliptic integrals of the first kink.", "category": "cond-mat_other" }, { "text": "Effects of an oscillating field on pattern formation in a ferromagnetic\n thin film: Analysis of patterns traveling at a low velocity: Magnetic domain patterns under an oscillating field is studied theoretically\nby using a simple Ising-like model. We propose two ways to investigate the\neffects of the oscillating field. The first one leads to a model in which\nrapidly oscillating terms are averaged out, and the model can explain the\nexistence of the maximum amplitude of the field for the appearance of patterns.\nThe second one leads to a model that includes the delay of the response to the\nfield, and the model suggests the existence of a traveling pattern which moves\nvery slowly compared with the time scale of the driving field.", "category": "cond-mat_other" }, { "text": "Fidelity and Quantum phase transition for the Heisenberg chain with the\n next-nearest-neighbor interaction: In this paper, we investigate the fidelity for the Heisenberg chain with the\nnext-nearest-neighbor interaction (or the $J_1-J_2$ model) and analyze its\nconnections with quantum phase transition. We compute the fidelity between the\nground states and find that the phase transition point of the $J_1-J_2$ model\ncan not be well characterized by the ground state fidelity for finite-size\nsystems. Instead, we introduce and calculate the fidelity between the first\nexcited states. Our results show that the quantum transition can be well\ncharacterized by the fidelity of the first excited state even for a small-size\nsystem.", "category": "cond-mat_other" }, { "text": "Quantum levitation of nanoparticles seen with ultracold neutrons: Analyzing new experiments with ultracold neutrons (UCNs) we show that\nphysical adsorption of nanoparticles/nano-droplets, levitating in high-excited\nstates in a deep and broad potential well formed by van der\nWaals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of\nfundamental interactions, neutron, surface and nanoparticle physics. Accounting\nfor the interaction of UCNs with nanoparticles explains a recently discovered\nintriguing small heating of UCNs in traps. It might be relevant to the striking\nconflict of the neutron lifetime experiments with smallest reported\nuncertainties by adding false effects there.", "category": "cond-mat_other" }, { "text": "Fast partial decoherence of a superconducting flux qubit in a spin bath: The superconducting flux qubit has two quantum states with opposite magnetic\nflux. Environment of nuclear spins can find out the direction of the magnetic\nflux after a decoherence time $\\tau_0$ inversely proportional to the magnitude\nof the flux and the square root of the number of spins. When the Hamiltonian of\nthe qubit drives fast coherent Rabi oscillations between the states with\nopposite flux, then flux direction is flipped at a constant rate $\\omega$ and\nthe decoherence time $\\tau=\\omega\\tau_0^2$ is much longer than $\\tau_0$.\nHowever, on closer inspection decoherence actually takes place on two\ntimescales. The long time $\\tau$ is a time of full decoherence but a part of\nquantum coherence is lost already after the short time $\\tau_0$. This fast\npartial decoherence biases coherent flux oscillations towards the initial flux\ndirection and it can affect performance of the superconducting devices as\nqubits.", "category": "cond-mat_other" }, { "text": "Adiabatic self-trapped states in carbon nanotubes: We study here polaron (soliton) states of electrons or holes in a model\ndescribing carbon-type nanotubes. In the Hamiltonian of the system we take into\naccount the electron-phonon interaction that arises from the deformation\ndependencies of both the on-site and the hopping interaction energies. Using an\nadiabatic approximation, we derive the equations for self-trapped electron\nstates in zigzag nanotubes. We find the ground states of an electron in such a\nsystem and show that the polaron states can have different symmetries depending\non the strength of the electron-phonon coupling. Namely, at relatively weak\ncoupling the polarons possess quasi-one-dimensional (quasi-1D) properties and\nhave an azimuthal symmetry. When the coupling constant exceeds some critical\nvalue, the azimuthal symmetry breaks down and the polaron spreads out in more\nthan one dimension.\n We also study polarons that are formed by the electrons in the conducting\nband (or by holes in the valence band) in semiconducting carbon nanotubes. We\nshow that their properties are more complex than those of quasi-1D ground state\npolarons. In particular, polarons in semiconducting carbon nanotubes possess an\ninner structure: being self-trapped along the nanotube axis they exhibit some\nmodulations around the nanotube.", "category": "cond-mat_other" }, { "text": "Electrical conductivity in granular media and Branly's coherer: A simple\n experiment: We show how a simple laboratory experiment can illustrate certain electrical\ntransport properties of metallic granular media. At a low critical imposed\nvoltage, a transition from an insulating to a conductive state is observed.\nThis transition comes from an electro-thermal coupling in the vicinity of the\nmicrocontacts between grains where microwelding occurs. Our apparatus allows us\nto obtain an implicit determination of the microcontact temperature, which is\nanalogous to the use of a resistive thermometer. The experiment also\nillustrates an old problem, the explanation of Branly's coherer effect - a\nradio wave detector used for the first wireless radio transmission, and based\non the sensitivity of the metal fillings conductivity to an electromagnetic\nwave.", "category": "cond-mat_other" }, { "text": "Thermally induced rotons in two-dimensional dilute Bose gases: We show that roton-like excitations are thermally induced in a\ntwo-dimensional dilute Bose gas as a consequence of the strong phase\nfluctuations in two dimensions. At low momentum, the roton-like excitations\nlead for small enough temperatures to an anomalous phonon spectrum with a\ntemperature dependent exponent reminiscent of the Kosterlitz-Thouless\ntransition. Despite the anomalous form of the energy spectrum, it is shown that\nthe corresponding effective theory of vortices describes the usual\nKosterlitz-Thouless transition. The possible existence of an anomalous normal\nstate in a small temperature interval is also discussed.", "category": "cond-mat_other" }, { "text": "Self-similar space-filling sphere packings in three and four dimensions: Inversive geometry can be used to generate exactly self-similar space-filling\nsphere packings. We present a construction method in two dimensions and\ngeneralize it to search for packings in higher dimensions. We newly discover 29\nthree-dimensional and 13 four-dimensional topologies of which 10 and 5,\nrespectively, are bearings. To distinguish and characterize the packing\ntopologies, we numerically estimate their fractal dimensions and we analyze\ntheir contact networks.", "category": "cond-mat_other" }, { "text": "Influence of Exchange Scattering on Superfluid He-3 states in Nematic\n Aerogel: The superfluid state in bulk liquid $^3$He is realized in the form of A or B\nphases. Uniaxially anisotropic aerogel (nafen) stabilizes transition from the\nnormal to the polar superfluid state which on further cooling transitions to\nthe axipolar orbital glass state (Phys. Rev. Lett. {\\bf 115}, 165304 (2015)).\nThis is the case in nafen aerogel preplated by several atomic layers of $^4$He.\nWhen pure liquid $^3$He fills the same nafen aerogel a solid-like layer of\n$^3$He atoms coats the aerogel structure. The polar state is not formed anymore\nand a phase transition occurs directly to the axipolar phase (Phys. Rev. Lett.\n{\\bf 120}, 075301 (2018). The substitution of $^4$He by $^3$He atoms at the\naerogel surface changes the potential and adds the exchange scattering of\nquasiparticles on the aerogel strands. A calculation shows that both of these\neffects can decrease the degree of anisotropy of scattering and suppress the\npolar phase formation. The derived anisotropy of the spin diffusion coefficient\nin globally anisotropic aerogel is determined by the same parameter which\ncontrols the polar state emergence which allows one to check the effect of\nanisotropy change for different types of covering.", "category": "cond-mat_other" }, { "text": "Partially incoherent gap solitons in Bose-Einstein condensates: We construct families of incoherent matter-wave solitons in a repulsive\ndegenerate Bose gas trapped in an optical lattice (OL), i.e., gap solitons, and\ninvestigate their stability at zero and finite temperature, using the\nHartree-Fock-Bogoliubov equations. The gap solitons are composed of a coherent\ncondensate, and normal and anomalous densities of incoherent vapor co-trapped\nwith the condensate. Both intragap and intergap solitons are constructed, with\nchemical potentials of the components falling in one or different bandgaps in\nthe OL-induced spectrum. Solitons change gradually with temperature. Families\nof intragap solitons are completely stable (both in direct simulations, and in\nterms of eigenvalues of perturbation modes), while the intergap family may have\na very small unstable eigenvalue (nevertheless, they feature no instability in\ndirect simulations). Stable higher-order (multi-humped) solitons, and bound\ncomplexes of fundamental solitons are found too.", "category": "cond-mat_other" }, { "text": "Mechanisms limiting the coherence time of spontaneous magnetic\n oscillations driven by DC spin-polarized currents: The spin-transfer torque from a DC spin-polarized current can generate\nhighly-coherent magnetic precession in nanoscale magnetic-multilayer devices.\nBy measuring linewidths of spectra from the resulting resistance oscillations,\nwe argue that the coherence time can be limited at low temperature by thermal\ndeflections about the equilibrium magnetic trajectory, and at high temperature\nby thermally-activated transitions between dynamical modes. Surprisingly, the\ncoherence time can be longer than predicted by simple macrospin simulations.", "category": "cond-mat_other" }, { "text": "Electronic states in 1/1 Cd6Yb and 1/1 Cd6Ca: Relativistic, correlation,\n and structural effects: The electronic structure of the rational approximants 1/1 Cd6Yb and 1/1 Cd6Ca\nto the stable icosahedral CdYb and CdCa quasicrystals is studied by the\nfull-potential linear augmented plane wave method. A comparison is made between\nseveral structural models. We show that the (relativistic) spin-orbit (SO)\ninteraction and electronic correlations that are not described by the usual\nlocal density approximation, are essential for an accurate description of the\nelectronic structure. In particular, we show that the SO interaction is\nresponsible for a splitting of the Cd-4d and Yb-4f peaks, and that the\nexperimental peak positions can be reproduced by including a Hubbard U term in\nthe Hamiltonian [U(Cd) = 5.6 eV, U(Yb) = 3.1 eV]. Our results show very good\nagreement with a photo-emission (PE) spectrum of 1/1 Cd6Yb [R. Tamura, Y.\nMurao, S. Takeuchi, T. Kiss, T. Yokoya, and S. Shin, Phys. Rev. B 65, 224207\n(2002)] and a 350 eV PE spectrum of 1/1 Cd6Ca, which we present in this paper.\nWithout the relativistic and correlation effects even a qualitative agreement\nwith the PE spectra cannot be achieved.", "category": "cond-mat_other" }, { "text": "Magneto-optic far-infrared study of Sr$_{14}$Cu$_{24}$O$_{41}$: triplet\n excitations in chains: Using far-infrared spectroscopy we have studied the magnetic field and\ntemperature dependence of the spin gap modes in the chains of\nSr$_{14}$Cu$_{24}$O$_{41}$. Two triplet modes T$_1$ and T$_2$ were found in the\ncenter of the Brillouin zone at $\\Delta_1=9.65$ meV and $\\Delta_2=10.86$ meV in\nzero magnetic field. The T$_1$ mode was excited when the electric field vector\n${\\bf E}$ of the light was polarized along the b axis (perpendicular to the\nplanes of chains and ladders) and T$_2$ was excited for ${\\bf E}\\parallel {\\bf\na}$ (perpendicular to the chains and along the rungs). Up to the maximum\nmagnetic field of 18 T, applied along the chains, the electron $g$ factors of\nthese two modes were similar, $g_{1c}=2.049$ and $g_{2c}=2.044$. Full linewidth\nat half maximum for both modes was 1 cm$^{-1}$ (0.12 meV) at 4K and increased\nwith $T$. The temperature dependence of mode energies and line intensities was\nin agreement with the inelastic neutron scattering results from two groups\n[Matsuda {\\it et al.}, Phys. Rev. B {\\bf 59}, 1060 (1999) and Regnault {\\it et\nal.}, Phys. Rev. B {\\bf 59}, 1055 (1999)]. The T$_1$ mode has not been observed\nby inelastic neutron scattering in the points of the $k$-space equivalent to\nthe center of the Brillouin zone. Our study indicates that the zone structure\nmodel of magnetic excitations of Sr$_{14}$Cu$_{24}$O$_{41}$ must be modified to\ninclude a triplet mode at 9.65 meV in the center of the magnetic Brillouin\nzone.", "category": "cond-mat_other" }, { "text": "Low-frequency noise and tunnelling magnetoresistance in\n Fe(110)/MgO(111)/Fe(110) epitaxial magnetic tunnel junctions: We report on tunnelling magnetoresistance (TMR), current-voltage (IV)\ncharacteristics and low frequency noise in epitaxially grown\nFe(110)/MgO(111)/Fe(110) magnetic tunnel junctions (MTJs) with dimensions from\n2x2 to 20x20 um2. The evaluated MgO energy barrier (0.50+/-0.08 eV), the\nbarrier width (13.1+/-0.5 angstrom) as well as the resistance times area\nproduct (7+/-1 Mohmsum2) show relatively small variation, confirming a high\nquality epitaxy and uniformity of all MTJs studied. The noise power, though\nexhibiting large variation, was observed to be roughly anticorrelated with the\nTMR. Surprisingly, for the largest junctions we observed a strong enhancement\nof the normalized low-frequency noise in the antiparallel magnetic\nconfiguration. This behaviour could be related to an interplay between the\nmagnetic state and the local barrier defects structure of the epitaxial MTJs", "category": "cond-mat_other" }, { "text": "Physical and mathematical justification of the numerical Brillouin zone\n integration of the Boltzmann rate equation by Gaussian smearing: Scatterings of electrons at quasiparticles or photons are very important for\nmany topics in solid state physics, e.g., spintronics, magnonics or photonics,\nand therefore a correct numerical treatment of these scatterings is very\nimportant. For a quantum-mechanical description of these scatterings Fermi's\ngolden rule is used in order to calculate the transition rate from an initial\nstate to a final state in a first-order time-dependent perturbation theory. One\ncan calculate the total transition rate from all initial states to all final\nstates with Boltzmann rate equations involving Brillouin zone integrations. The\nnumerical treatment of these integrations on a finite grid is often done via a\nreplacement of the Dirac delta distribution by a Gaussian. The Dirac delta\ndistribution appears in Fermi's golden rule where it describes the energy\nconservation among the interacting particles. Since the Dirac delta\ndistribution is a not a function it is not clear from a mathematical point of\nview that this procedure is justified. We show with physical and mathematical\narguments that this numerical procedure is in general correct, and we comment\non critical points.", "category": "cond-mat_other" }, { "text": "On the evolution of higher order fluxes in non-equilibrium\n thermodynamics: The connection between the balance structure of the evolution equations of\nhigher order fluxes and different forms of the entropy current is investigated\non the example of rigid heat conductors. Compatibility conditions of the\ntheories are given. Thermodynamic closure relations are derived.", "category": "cond-mat_other" }, { "text": "Quantum fluctuations of a vortex in a dilute Bose-Einstein condensate: A vortex in a quasi two-dimensional Bose-Einstein condensate is subject to\nthe Magnus force and can be effectively described as a planar particle in a\nuniform magnetic field. Quantization of this effective particle leads to the\nlowest Landau level where the most localized wave function is a gaussian. In\nthis gaussian state vortex position seems to fluctuate with an average\nmagnitude set by the magnetic width of the gaussian. We readdress this problem\nusing the number-conserving version of the Bogoliubov theory. We find that the\nBogoliubov mode that might be interpreted as a fluctuation of vortex position\nactually does not contribute to position fluctuation at all. The only non-zero\ncontribution comes from phonons but it is an order of magnitude less than the\nsimple estimate, based on the magnetic width of the effective gaussian wave\npacket.", "category": "cond-mat_other" }, { "text": "Ground State of Quantum Jahn-Teller Model: Selftrapping vs Correlated\n Phonon-assisted Tunneling: Ground state of the quantum Jahn-Teller model with broken rotational symmetry\nwas investigated by the variational approach in two cases: a lattice and a\nlocal ones. Both cases differ by the way of accounting for the nonlinearity\nhidden in the reflection-symmetric Hamiltonian. In spite of that the ground\nstate energy in both cases shows the same features: there appear two regions of\nmodel parameters governing the ground state: the region of dominating\nselftrapping modified by the quantum effects and the region of dominating\nphonon-assisted tunneling (antiselftrapping). In the local case (i) the effect\nof quantum fluctuations and anharmonicity due to the two-mode correlations is\nup to two orders larger than contributions due to the reflection effects of\ntwo-center wave function; (ii) the variational results for the ground state\nenergy were compared with exact numerical results. The coincidence is the\nbetter the more far away from the transition region at the E$\\otimes$e symmetry\nwhere the variational approach fails.", "category": "cond-mat_other" }, { "text": "On the effect of superfluid flows on the interaction of microwaves with\n He II: The paper proposes a possible mechanism of interaction of microwaves with\nsuperfluid helium that results in an experimentally observed narrow peak of\nmicrowave absorption on the frequencies by the order of the roton frequency.\nThe obtained microwave photon absorption coefficient depends on the local\nequilibrium distribution function which is established due to fast roton-roton\nand roton-phonon interactions. With the availability of superfluid flows, the\nlocal equilibrium distribution function depends on their velocity. The critical\nvelocity of the flows, at which the absorption of microwaves is replaced by\ntheir radiation, is found.", "category": "cond-mat_other" }, { "text": "Momentum distribution dynamics of a Tonks-Girardeau gas: Bragg\n reflections of a quantum many-body wavepacket: The dynamics of the momentum distribution and the reduced single-particle\ndensity matrix (RSPDM) of a Tonks-Girardeau (TG) gas is studied in the context\nof Bragg-reflections of a many-body wavepacket. We find strong suppression of a\nBragg-reflection peak for a dense TG wavepacket; our observation illustrates\ndependence of the momentum distribution on the interactions/wavefunction\nsymmetry. The momentum distribution is calculated with a fast algorithm based\non a formula expressing the RSPDM via a dynamically evolving single-particle\nbasis.", "category": "cond-mat_other" }, { "text": "Velocity correlations in dense granular flows: Velocity fluctuations of grains flowing down a rough inclined plane are\nexperimentally studied. The grains at the free surface exhibit fluctuating\nmotions, which are correlated over few grains diameters. The characteristic\ncorrelation length is shown to depend on the inclination of the plane and not\non the thickness of the flowing layer. This result strongly supports the idea\nthat dense granular flows are controlled by a characteristic length larger than\nthe particle diameter.", "category": "cond-mat_other" }, { "text": "First-principles calculations of the phonon dispersion curves of H on\n Pt(111): We have calculated the surface phonon dispersion curves for H on Pt(111),\nusing first-principles, total energy calculations based on a mixed-basis set\nand norm-conserving pseudopotentials. Linear response theory and the harmonic\napproximation are invoked. For one monolayer of H in the preferred adsorption\nsite (fcc hollow) vibrational modes polarized parallel and perpendicular to the\nsurface are found, respectively, at 73.5 meV and 142.6 meV, at the Γ point\nof the surface Brillouin zone. The degeneracy of the parallel mode is lifted at\nthe zone boundaries, yielding energies of 69.6 meV and 86.3 meV at the M point\nand 79.4 meV and 80.8 meV at the K point. The dispersion curves for H\nadsorption at the hcp hollow site differ only slightly from the above. In\neither case, H adsorption has considerable impact on the substrate modes; in\nparticular the surface mode in the gap in the bulk phonon spectrum (around M\npoint) is pushed into the bulk band. For on-top H adsorption, modes polarized\nparallel and perpendicular to the surface have respective energies of 47.4 meV\nand 277.2 meV, at the Γ point. The former disperses to 49.1 meV and 59.5\nmeV at the M point and to 56 meV and 56.7 meV at the K point. The H vibrational\nmode polarized perpendicular to the surface shows little dispersion, in all\nthree cases considered. Insights are obtained from the hybridization of the H\nand Pt electronic states.", "category": "cond-mat_other" }, { "text": "Self-focusing magnetostatic beams in thin magnetic films: The possibility of generation of stable self-focusing beams in in-plane\nmagnetized thin magnetic films is considered and theoretical conditions for the\nexistence of such localized solutions are discussed. It is shown that for the\ndefinite direction between static magnetizing field and preferential direction\nof radiation from microwave antenna the problem reduces to the one-dimensional\nnonlinear Schroedinger equation. For such angles it is possible to generate\nstable self-focusing beams. Particular values of beam width and propagation\nangles versus magnitude of magnetizing field are calculated in order to suggest\nthe realistic experimental setup for the observation of discovered effect.", "category": "cond-mat_other" }, { "text": "Heteronuclear molecules in an optical dipole trap: We report on the creation and characterization of heteronuclear KRb Feshbach\nmolecules in an optical dipole trap. Starting from an ultracold gas mixture of\nK-40 and Rb-87 atoms, we create as many as 25,000 molecules at 300 nK by rf\nassociation. Optimizing the association process, we achieve a conversion\nefficiency of 25%. We measure the temperature dependence of the rf association\nprocess and find good agreement with a phenomenological model that has\npreviously been applied to Feshbach molecule creation by slow magnetic-field\nsweeps. We also present a measurement of the binding energy of the\nheteronuclear molecules in the vicinity of the Feshbach resonance and provide\nevidence for Feshbach molecules as deeply bound as 26 MHz.", "category": "cond-mat_other" }, { "text": "Coherence-enhanced imaging of a degenerate Bose gas: We present coherence-enhanced imaging, an in situ technique that uses Raman\nsuperradiance to probe the spatial coherence properties of an ultracold gas.\nApplying this method, we obtain a spatially resolved measurement of the\ncondensate number and more generally, of the first-order spatial correlation\nfunction in a gas of $^{87}$Rb atoms. We observe the enhanced decay of\npropagating spin gratings in high density regions of a Bose condensate, a decay\nwe ascribe to collective, non-linear atom-atom scattering. Further, we directly\nobserve spatial inhomogeneities that arise generally in the course of extended\nsample superradiance.", "category": "cond-mat_other" }, { "text": "Spectrum and Screening cloud in the central spin model: We consider an electronic spin in a quantum dot, coupled to the surrounding\nnuclear spins via inhomogeneous antiferromagnetic hyperfine interactions and\nsubject to a uniform field, which is described by Gaudin's central spin model.\nWe study spectral properties, the two-point correlation functions, and the\nmagnetization profile in the ground state and in low-lying excited states,\nwhich characterizes the structure of the cloud of nuclear spins screening the\nelectron spin. A close connection to the pair occupation probability in the\nBCS-model is established. Using the exact Bethe Ansatz solution of that model\nand arguments of integrability, we can distinguish between contributions from\npurely classical physics and from quantum fluctuations.", "category": "cond-mat_other" }, { "text": "The role of the spin in quasiparticle interference: Quasiparticle interference patterns measured by scanning tunneling microscopy\n(STM) can be used to study the local electronic structure of metal surfaces and\nhigh temperature superconductors. Here, we show that even in non-magnetic\nsystems the spin of the quasiparticles can have a profound effect on the\ninterference patterns. On Bi(110), where the surface state bands are not\nspin-degenerate, the patterns are not related to the dispersion of the\nelectronic states in a simple way. In fact, the features which are expected for\nthe spin-independent situation are absent and the observed interference\npatterns can only be interpreted by taking spin-conserving scattering events\ninto account.", "category": "cond-mat_other" }, { "text": "Multiple time scales and the exponential Ornstein-Uhlenbeck stochastic\n volatility model: We study the exponential Ornstein-Uhlenbeck stochastic volatility model and\nobserve that the model shows a multiscale behavior in the volatility\nautocorrelation. It also exhibits a leverage correlation and a probability\nprofile for the stationary volatility which are consistent with market\nobservations. All these features make the model quite appealing since it\nappears to be more complete than other stochastic volatility models also based\non a two-dimensional diffusion. We finally present an approximate solution for\nthe return probability density designed to capture the kurtosis and skewness\neffects.", "category": "cond-mat_other" }, { "text": "Coherent control theory and experiment of optical phonons in diamond: The coherent control of optical phonons has been experimentally demonstrated\nin various physical systems. While the transient dynamics for optical phonons\ncan be explained by phenomenological models, the coherent control experiment\ncannot be explained due to the quantum interference. Here, we theoretically\npropose the generation and detection processes of the optical phonons and\nexperimentally confirm our theoretical model using the diamond optical phonon\nby the double-pump-probe type experiment.", "category": "cond-mat_other" }, { "text": "Propagation of self-localised Q-ball solitons in the $^3$He universe: In relativistic quantum field theories, compact objects of interacting bosons\ncan become stable owing to conservation of an additive quantum number $Q$.\nDiscovering such $Q$-balls propagating in the Universe would confirm\nsupersymmetric extensions of the standard model and may shed light on the\nmysteries of dark matter, but no unambiguous experimental evidence exists. We\nreport observation of a propagating long-lived $Q$-ball in superfluid $^3$He,\nwhere the role of $Q$-ball is played by a Bose-Einstein condensate of magnon\nquasiparticles. We achieve accurate representation of the $Q$-ball Hamiltonian\nusing the influence of the number of magnons, corresponding to the charge $Q$,\non the orbital structure of the superfluid $^3$He order parameter. This\nrealisation supports multiple coexisting $Q$-balls which in future allows\nstudies of $Q$-ball dynamics, interactions, and collisions.", "category": "cond-mat_other" }, { "text": "Superfluid Edge Dislocation: Transverse Quantum Fluid: Recently, it has been argued by Kuklov et al., that unusual features\nassociated with the superflow-through-solid effect observed in solid He4 can be\nexplained by unique properties of dilute distribution of superfluid edge\ndislocations. We demonstrate that stability of supercurrents controlled by\nquantum phase slips (instantons), and other exotic infrared properties of the\nsuperfluid dislocations readily follow from a one-dimensional quantum liquid\ndistinguished by an effectively infinite compressibility (in the absence of\nPeierls potential) associated with the edge dislocation's ability to climb.\nThis establishes a new class of quasi-one-dimensional superfluid states that\nremain stable and long-range ordered despite their low dimensionality. We\npropose an experiment to test our mass-current--pressure characteristic\nprediction.", "category": "cond-mat_other" }, { "text": "Generalisation of Gilbert damping and magnetic inertia parameter as a\n series of higher-order relativistic terms: The phenomenological Landau-Lifshitz-Gilbert (LLG) equation of motion remains\nas the cornerstone of contemporary magnetisation dynamics studies, wherein the\nGilbert damping parameter has been attributed to first-order relativistic\neffects. To include magnetic inertial effects the LLG equation has previously\nbeen extended with a supplemental inertia term and the arising inertial\ndynamics has been related to second-order relativistic effects. Here we start\nfrom the relativistic Dirac equation and, performing a Foldy-Wouthuysen\ntransformation, derive a generalised Pauli spin Hamiltonian that contains\nrelativistic correction terms to any higher order. Using the Heisenberg\nequation of spin motion we derive general relativistic expressions for the\ntensorial Gilbert damping and magnetic inertia parameters, and show that these\ntensors can be expressed as series of higher-order relativistic correction\nterms. We further show that, in the case of a harmonic external driving field,\nthese series can be summed and we provide closed analytical expressions for the\nGilbert and inertial parameters that are functions of the frequency of the\ndriving field.", "category": "cond-mat_other" }, { "text": "Fundamental dissipation due to bound fermions in the zero-temperature\n limit: The ground state of a fermionic condensate is well protected against\nperturbations in the presence of an isotropic gap. Regions of gap suppression,\nsurfaces and vortex cores which host Andreev-bound states, seemingly lift that\nstrict protection. Here we show that the role of bound states is more subtle:\nwhen a macroscopic object moves in superfluid $^3$He at velocities exceeding\nthe Landau critical velocity, little to no bulk pair breaking takes place,\nwhile the damping observed originates from the bound states covering the moving\nobject. We identify two separate timescales that govern the bound state\ndynamics, one of them much longer than theoretically anticipated, and show that\nthe bound states do not interact with bulk excitations.", "category": "cond-mat_other" }, { "text": "Effective magnetic fields in degenerate atomic gases induced by light\n beams with orbital angular momenta: We investigate the influence of two resonant laser beams on the mechanical\nproperties of degenerate atomic gases. The control and probe beams of light are\nconsidered to have Orbital Angular Momenta (OAM) and act on the three-level\natoms in the Electromagnetically Induced Transparency (EIT) configuration. The\ntheory is based on the explicit analysis of the quantum dynamics of cold atoms\ncoupled with two laser beams. Using the adiabatic approximation, we obtain an\neffective equation of motion for the atoms driven to the dark state. The\nequation contains a vector potential type interaction as well as an effective\ntrapping potential. The effective magnetic field is shown to be oriented along\nthe propagation direction of the control and probe beams containing OAM. Its\nspatial profile can be controlled by choosing proper laser beams. We\ndemonstrate how to generate a constant effective magnetic field, as well as a\nfield exhibiting a radial distance dependence. The resulting effective magnetic\nfield can be concentrated within a region where the effective trapping\npotential holds the atoms. The estimated magnetic length can be considerably\nsmaller than the size of the atomic cloud.", "category": "cond-mat_other" }, { "text": "Exact soliton solution of Spin Chain with a external magnetic field in\n linear wave background: Employing a simple, straightforward Darboux transformation we construct exact\nN-soliton solution for anisotropic spin chain driven by a external magnetic\nfield in linear wave background. As a special case the explicit one- and\ntwo-soliton solution dressed by the linear wave corresponding to magnon in\nquantum theory is obtained analytically and its property is discussed in\ndetail. The dispersion law, effective soliton mass, and the energy of each\nsoliton are investigated as well. Our result show that the stability criterion\nof soliton is related with anisotropic parameter and the amplitude of the\nlinear wave.", "category": "cond-mat_other" }, { "text": "Mass flux and solid growth in solid 4He: 60 mK - 700 mK: We use the thermo-mechanical effect to create a chemical potential difference\nbetween two liquid reservoirs connected to each other through Vycor rods in\nseries with solid hcp 4He to confirm that a DC flux of atoms takes place below\n600 mK, but find that the flux falls abruptly in the vicinity of 80 mK. It is\nimpossible to add density to a solid freshly made at 60 mK and samples freshly\nmade at 60 mK do not allow mass flux, even when raised in temperature to 200\nmK. Solids created above 300 mK and cooled to 60 mK accept added density and\ndemonstrate finite mass flux.", "category": "cond-mat_other" }, { "text": "Range separation combined with the Overhauser model: Application to the\n H$_2$ molecule along the dissociation curve: The combination of density-functional theory with other approaches to the\nmany-electron problem through the separation of the electron-electron\ninteraction into a short-range and a long-range contribution (range separation)\nis a successful strategy, which is raising more and more interest in recent\nyears. We focus here on a range-separated method in which only the short-range\ncorrelation energy needs to be approximated, and we model it within the\n\"extended Overhauser approach\". We consider the paradigmatic case of the H$_2$\nmolecule along the dissociation curve, finding encouraging results. By means of\nvery accurate variational wavefunctions, we also study how the effective\nelectron-electron interaction appearing in the Overhauser model should be in\norder to yield the exact correlation energy for standard Kohn-Sham density\nfunctional theory.", "category": "cond-mat_other" }, { "text": "p-wave Feshbach molecules: We have produced and detected molecules using a p-wave Feshbach resonance\nbetween 40K atoms. We have measured the binding energy and lifetime for these\nmolecules and we find that the binding energy scales approximately linearly\nwith magnetic field near the resonance. The lifetime of bound p-wave molecules\nis measured to be 1.0 +/- 0.1 ms and 2.3 +/- 0.2 ms for the m_l = +/- 1 and m_l\n= 0 angular momentum projections, respectively. At magnetic fields above the\nresonance, we detect quasi-bound molecules whose lifetime is set by the\ntunneling rate through the centrifugal barrier.", "category": "cond-mat_other" }, { "text": "Anyons from fermions with conventional two-body interactions: Emergent anyons are the key elements of the topological quantum computation\nand topological quantum memory. We study a two-component fermion model with\nconventional two-body interaction in an open boundary condition and show that\nseveral subsets in the low-lying excitations obey the same fusion rules as\nthose of the toric code model. Those string-like non-local excitations in a\ngiven subset obey mutual semionic statistics. We show how to peel off one of\nsuch subset from other degenerate subsets and manipulate anyons in cold dipolar\nFermi atoms or cold dipolar fermionic heteronuclear molecules in optical\nlattices by means of the established techniques.", "category": "cond-mat_other" }, { "text": "Spin motive forces due to magnetic vortices and domain walls: We study spin motive forces, i.e, spin-dependent forces, and voltages induced\nby time-dependent magnetization textures, for moving magnetic vortices and\ndomain walls. First, we consider the voltage generated by a one-dimensional\nfield-driven domain wall. Next, we perform detailed calculations on\nfield-driven vortex domain walls. We find that the results for the voltage as a\nfunction of magnetic field differ between the one-dimensional and vortex domain\nwall. For the experimentally relevant case of a vortex domain wall, the\ndependence of voltage on field around Walker breakdown depends qualitatively on\nthe ratio of the so-called $\\beta$-parameter to the Gilbert damping constant,\nand thus provides a way to determine this ratio experimentally. We also\nconsider vortices on a magnetic disk in the presence of an AC magnetic field.\nIn this case, the phase difference between field and voltage on the edge is\ndetermined by the $\\beta$ parameter, providing another experimental method to\ndetermine this quantity.", "category": "cond-mat_other" }, { "text": "Magnetic Domain Wall Pumping by Spin Transfer Torque: We show that spin transfer torque from direct spin-polarized current applied\nparallel to a magnetic domain wall (DW) induces DW motion in a direction\nindependent of the current polarity. This unidirectional response of the DW to\nspin torque enables DW pumping: long-range DW displacement driven by\nalternating current. Our numerical simulations reveal that DW pumping can be\nresonantly amplified through excitation of internal degrees of freedom of the\nDW by the current.", "category": "cond-mat_other" }, { "text": "Heteronuclear quantum gas mixtures: This PhD tutorial article is a review of our experiments on heteronuclear\nquantum gas mixtures at the University of Hamburg. We introduce basic\nproperties of trapped Fermi-Bose mixtures and demonstrate the achievement of\nlarge quantum degenerate mixtures of 40K and 87Rb. Using heteronuclear Feshbach\nresonances, we show how the heteronuclear interaction can be tuned, allowing us\nto induce phase separation and collapse for large repulsive and attractive\ninteractions, respectively. We realize Fermi-Bose mixtures in 3D optical\nlattices as a novel quantum many-body system and study coherence properties of\nthe mixture. Combining our experiments on lattices and Feshbach resonances, we\npresent the first realization of ultracold heteronuclear Feshbach molecules.\nThe molecules are created at individual sites of a 3D optical lattice. We\ndiscuss lifetime, binding energy and rf association efficiency in terms of a\nuniversal model and give an outlook for possible future developments.", "category": "cond-mat_other" }, { "text": "Dynamics of a Bright Soliton in Bose-Einstein condensates with\n Time-Dependent Atomic Scattering Length in an Expulsive Parabolic Potential: We present a family of exact solutions of one-dimensional nonlinear\nSchr\\\"odinger equation, which describe the dynamics of a bright soliton in\nBose-Einstein condensates with the time-dependent interatomic interaction in an\nexpulsive parabolic potential. Our results show that, under the safe range of\nparameters, the bright soliton can be compressed into very high local matter\ndensities by increasing the absolute value of atomic scattering length, which\ncan provide an experimental tool for investigating the range of validity of the\none-dimensional Gross-Pitaevskii equation. We also find that the number of\natoms in the bright soliton keeps dynamic stability: a time-periodic atomic\nexchange is formed between the bright soliton and the background.", "category": "cond-mat_other" }, { "text": "Cross-sections of Andreev scattering by quantized vortex rings in 3He-B: We studied numerically the Andreev scattering cross-sections of\nthree-dimensional isolated quantized vortex rings in superfluid 3He-B at\nultra-low temperatures. We calculated the dependence of the cross-section on\nthe ring's size and on the angle between the beam of incident thermal\nquasiparticle excitations and the direction of the ring's motion. We also\nintroduced, and investigated numerically, the cross-section averaged over all\npossible orientations of the vortex ring; such a cross-section may be\nparticularly relevant for the analysis of experimental data. We also analyzed\nthe role of screening effects for Andreev reflection of quasiparticles by\nsystems of vortex rings. Using the results obtained for isolated rings we found\nthat the screening factor for a system of unlinked rings depends strongly on\nthe average radius of the vortex ring, and that the screening effects increase\nwith decreasing the rings' size.", "category": "cond-mat_other" }, { "text": "Modelling the term structure of interest rates \u00e1 la\n Heath-Jarrow-Morton but with non Gaussian fluctuations: We consider a generalization of the Heath Jarrow Morton model for the term\nstructure of interest rates where the forward rate is driven by Paretian\nfluctuations. We derive a generalization of It\\^{o}'s lemma for the calculation\nof a differential of a Paretian stochastic variable and use it to derive a\nStochastic Differential Equation for the discounted bond price. We show that it\nis not possible to choose the parameters of the model to ensure absence of\ndrift of the discounted bond price. Then we consider a Continuous Time Random\nWalk with jumps driven by Paretian random variables and we derive the large\ntime scaling limit of the jump probability distribution function (pdf). We show\nthat under certain conditions defined in text the large time scaling limit of\nthe jump pdf in the Fourier domain is \\tilde{omega}_t(k,t) \\sim \\exp{-K/(\\ln(k\nt))^2} and is different from the case of a random walk with Gaussian\nfluctuations. We also derive the master equation for the jump pdf and discuss\nthe relation of the master equation to Distributed Order Fractional Diffusion\nEquations.", "category": "cond-mat_other" }, { "text": "High domain wall velocities induced by current in ultrathin Pt/Co/AlOx\n wires with perpendicular magnetic anisotropy: Current-induced domain wall (DW) displacements in an array of ultrathin\nPt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly\nobserved by wide field Kerr microscopy. DWs in all wires in the array were\ndriven simultaneously and their displacement on the micrometer-scale was\ncontrolled by the current pulse amplitude and duration. At the lower current\ndensities where DW displacements were observed (j less than or equal to 1.5 x\n10^12 A/m^2), the DW motion obeys a creep law. At higher current density (j =\n1.8 x 10^12 A/m^2), zero-field average DW velocities up to 130 +/- 10 m/s were\nrecorded.", "category": "cond-mat_other" }, { "text": "Strongly Interacting Atoms and Molecules in a 3D Optical Lattice: We report on the realization of a strongly interacting quantum degenerate gas\nof fermionic atoms in a three-dimensional optical lattice. We prepare a\nband-insulating state for a two-component Fermi gas with one atom per spin\nstate per lattice site. Using a Feshbach resonance, we induce strong\ninteractions between the atoms. When sweeping the magnetic field from the\nrepulsive side towards the attractive side of the Feshbach resonance we induce\na coupling between Bloch bands leading to a transfer of atoms from the lowest\nband into higher bands. Sweeping the magnetic field across the Feshbach\nresonance from the attractive towards the repulsive side leads to two-particle\nbound states and ultimately to the formation of molecules. From the fraction of\nformed molecules we determine the temperature of the atoms in the lattice.", "category": "cond-mat_other" }, { "text": "Density modulations in an elongated Bose-Einstein condensate released\n from a disordered potential: We observe large density modulations in time-of-flight images of elongated\nBose-Einstein condensates, initially confined in a harmonic trap and in the\npresence of weak disorder. The development of these modulations during the\ntime-of-flight and their dependence with the disorder are investigated. We\nrender an account of this effect using numerical and analytical calculations.\nWe conclude that the observed large density modulations originate from the weak\ninitial density modulations induced by the disorder, and not from initial phase\nfluctuations (thermal or quantum).", "category": "cond-mat_other" }, { "text": "On surface plasmon polariton wavepacket dynamics in metal-dielectric\n heterostructures: The WKB equations for dynamics of the surface plasmon polariton (SPP)\nwavepacket are studied. The dispersion law for the SPP in the metal-dielectric\nheterostructure with varying thickness of a perforated dielectric layer is\nrigorously calculated and investigated using the scattering matrix method. Two\nchannels of the SPP wavepacket optical losses related to the absorption in a\nmetal and to the SPP leakage are analyzed. It is shown that change of the\ndielectric layer thickness acts on the SPP as an external force leading to\nevolution of its quasimomentum and to the wavepacket reversal or even to the\noptical Bloch oscillations (BO). Properties of these phenomena are investigated\nand discussed. Typical values of the BO amplitude are about tens of microns and\nthe period is around tens or hundreds of femtoseconds.", "category": "cond-mat_other" }, { "text": "Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb: Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb\nare presented and analyzed in terms of current models of charge conversion at a\nsuperconductor-ferromagnet interface. We investigate the influence of surface\ntransparency, and study the crossover from ballistic to diffusive transport\nregime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample\nwith Curie temperature Tc of 5.4 K allowed the determination of\nspin-polarization when the ferromagnetic phase transition temperature is\ncrossed. We find a striking difference between the temperature dependence of\nthe local spin polarization and of the macroscopic magnetization, and\ndemonstrate that nanoscale clusters with magnetization close to the saturated\nvalue are present even well above the magnetic phase transition temperature.", "category": "cond-mat_other" }, { "text": "Phase diagram of a Bose gas near a wide Feshbach resonance: In this paper, we study the phase diagram of a homogeneous Bose gas with a\nrepulsive interaction near a wide Feshbach resonance at zero temperature. The\nBose-Einstein-condensation (BEC) state of atoms is a metastable state. When the\nscattering length $a$ exceeds a critical value depending on the atom density\n$n$, $na^3>0.035$, the molecular excitation energy is imaginary and the atomic\nBEC state is dynamically unstable against molecule formation. The BEC state of\ndiatomic molecules has lower energy, where the atomic excitation is gapped and\nthe molecular excitation is gapless. However when the scattering length is\nabove another critical value, $na^3>0.0164$, the molecular BEC state becomes a\nunstable coherent mixture of atoms and molecules. In both BEC states, the\nbinding energy of diatomic molecules is reduced due to the many-body effect.", "category": "cond-mat_other" }, { "text": "Simple derivation of the frequency dependent complex heat capacity: This paper gives a simple derivation of the well-known expression of the\nfrequency dependent complex heat capacity in modulated temperature experiments.\nIt aims at clarified again that the generalized calorimetric susceptibility is\nonly due to the non-equilibrium behaviour occurring in the vicinity of\nthermodynamic equilibrium of slow internal degrees of freedom of a sample when\nthe temperature oscillates at a well determined frequency.", "category": "cond-mat_other" }, { "text": "PT-Symmetric Electronics: We show both theoretically and experimentally that a pair of inductively\ncoupled active LRC circuits (dimer), one with amplification and another with an\nequivalent amount of attenuation, display all the features which characterize a\nwide class of non-Hermitian systems which commute with the joint parity-time PT\noperator: typical normal modes, temporal evolution, and scattering processes.\nUtilizing a Liouvilian formulation, we can define an underlying PT-symmetric\nHamiltonian, which provides important insight for understanding the behavior of\nthe system. When the PT-dimer is coupled to transmission lines, the resulting\nscattering signal reveals novel features which reflect the PT-symmetry of the\nscattering target. Specifically we show that the device can show two different\nbehaviors simultaneously, an amplifier or an absorber, depending on the\ndirection and phase relation of the interrogating waves. Having an exact\ntheory, and due to its relative experimental simplicity, PT-symmetric\nelectronics offers new insights into the properties of PT-symmetric systems\nwhich are at the forefront of the research in mathematical physics and related\nfields.", "category": "cond-mat_other" }, { "text": "Number statistics of molecules formed from ultra-cold atoms: We calculate the number statistics of a single-mode molecular field excited\nby photoassociation or via a Feshbach resonance from an atomic Bose-Einstein\ncondensate (BEC), a normal atomic Fermi gas and a Fermi system with pair\ncorrelations (BCS state). We find that the molecule formation from a BEC is a\ncollective process that leads for short times to a coherent molecular state in\nthe quantum optical sense. Atoms in a normal Fermi gas, on the other hand, are\nconverted into molecules independently of each other and result for short times\nin a molecular state analogous to that of a classical chaotic light source. The\nBCS situation is intermediate between the two and goes from producing an\nincoherent to a coherent molecular field with increasing gap parameter.", "category": "cond-mat_other" }, { "text": "Determination of anisotropic dipole moments in self-assembled quantum\n dots using Rabi oscillations: By investigating the polarization-dependent Rabi oscillations using\nphotoluminescence spectroscopy, we determined the respective transition dipole\nmoments of the two excited excitonic states |Ex> and |Ey> of a single\nself-assembled quantum dot that are nondegenerate due to shape anisotropy. We\nfind that the ratio of the two dipole moments is close to the physical\nelongation ratio of the quantum dot.", "category": "cond-mat_other" }, { "text": "Chern-number spin Hamiltonians for magnetic nano-clusters by DFT methods: Combining field-theoretical methods and ab-initio calculations, we construct\nan effective Hamiltonian with a single giant-spin degree of freedom, capable of\nthe describing the low-energy spin dynamics of ferromagnetic metal nanoclusters\nconsisting of up to a few tens of atoms. In our procedure, the magnetic moment\ndirection of the Kohn-Sham SDFT wave-function is constrained by means of a\npenalty functional, allowing us to explore the entire parameter space of\ndirections, and to extract the magnetic anisotropy energy and Berry curvature\nfunctionals. The average of the Berry curvature over all magnetization\ndirections is a Chern number - a topological invariant that can only take on\nvalues equal to multiples of one half, representing the dimension of the\nHilbert space of the effective spin system. The spin Hamiltonian is obtained by\nquantizing the classical anisotropy energy functional, after performing a\nchange of variables to a constant Berry curvature space. The purpose of this\narticle is to examine the impact of the topological effect from the Berry\ncurvature on the low-energy total-spin-system dynamics. To this end, we study\nsmall transition metal clusters: Co$_{n}$ ($n=2,...,5$), Rh$_{2}$, Ni$_{2}$,\nPd$_{2}$, Mn$_{x}$N$_{y}$, Co$_{3}$Fe$_{2}$.", "category": "cond-mat_other" }, { "text": "3He on preplated graphite: By using the diffusion Monte Carlo method, we obtained the full phase diagram\nof $^3$He on top of graphite preplated with a solid layer of $^4$He. All the\n$^4$He atoms of the substrate were explicitly considered and allowed to move\nduring the simulation. We found that the ground state is a liquid of density\n0.007 $\\pm$ 0.001 \\AA$^{-2}$, in good agreement with available experimental\ndata. This is significantly different from the case of $^3$He on clean\ngraphite, in which both theory and experiment agree on the existence of a\ngas-liquid transition at low densities. Upon an increase in $^3$He density, we\npredict a first-order phase transition between a dense liquid and a registered\n7/12 phase, the 4/7 phase being found metastable in our calculations. At larger\nsecond-layer densities, a final transition is produced to an incommensurate\ntriangular phase.", "category": "cond-mat_other" }, { "text": "Dipole moments from atomic-number-dependent potentials in analytic\n density-functional theory: Molecular dipole moments of analytic density-functional theory are\ninvestigated. The effect of element-dependent exchange potentials on these\nmoments are examined by comparison with conventional quantum-chemical methods\nand experiment for the subset of the extended G2 set of molecules that have\nnonzero dipole moment. Fitting the Kohn-Sham [Phys. Rev. 140, A1133 (1965)]\npotential itself makes a mean absolute error of less than 0.1 Debye. Variation\nof alpha (Slater's [Phys. Rev. 81, 385 (1951)] exchange parameter) values has\nfar less effect on dipole moments than on energies. It is argued that in\nvariable alpha methods one should choose the smaller of the two rather than the\ngeometric mean of the two alpha values for the heteroatomic part of the\nlinear-combination-atomic-orbital density. Calculations on the dipole moment of\nNH2(CH)24NO2 are consistent with earlier calculations and show that varying the\ndifferences between alpha values for atoms with different atomic numbers has\nonly short-ranged electrostatic effects.", "category": "cond-mat_other" }, { "text": "Terahertz Kerr effect: We have observed optical birefringence in liquids induced by single-cycle THz\npulses with field strengths exceeding 100 kV/cm. The induced change in\npolarization is proportional to the square of the THz electric field. The\ntime-dependent THz Kerr signal is composed of a fast electronic response that\nfollows the individual cycles of the electric field and a slow exponential\nresponse associated with molecular orientation.", "category": "cond-mat_other" }, { "text": "Efficient unidirectional nanoslit couplers for surface plasmons: Plasmonics is based on surface plasmon polariton (SPP) modes which can be\nlaterally confined below the diffraction limit, thereby enabling ultracompact\noptical components. In order to exploit this potential, the fundamental\nbottleneck of poor light-SPP coupling must be overcome. In established SPP\nsources (using prism, grating} or nanodefect coupling) incident light is a\nsource of noise for the SPP, unless the illumination occurs away from the\nregion of interest, increasing the system size and weakening the SPP intensity.\nBack-side illumination of subwavelength apertures in optically thick metal\nfilms eliminates this problem but does not ensure a unique propagation\ndirection for the SPP. We propose a novel back-side slit-illumination method\nbased on drilling a periodic array of indentations at one side of the slit. We\ndemonstrate that the SPP running in the array direction can be suppressed, and\nthe one propagating in the opposite direction enhanced, providing localized\nunidirectional SPP launching.", "category": "cond-mat_other" }, { "text": "Numerical study of gas dynamic processes in conditions of silver\n nanocluster deposition experiments: In this paper, experiments on the deposition of silver nanoclusters are\nanalysed numerically using improved DSMC method. These experiments were made in\nthe Institute of Thermophysics SB RAS recent years, in the context of the\ndevelopment of bactericidal nanocomposite coatings deposition technology. In\nthis paper we analyze the gas-dynamic effects in experimental conditions: the\nparameters of the gas stream from the silver vapor source, the flow of silver\nvapors inside the source and in the outflowing jet under different conditions,\nthe movement of silver nanoclusters of different masses (up to 1024 atoms) in\nbuffer gas, expecting different places of nanocluster formation in a source.\nThe simulations revealed a strong nonisothermal state of the source, which was\nlater confirmed experimentally, the site of nanocluster nulceus formation in a\nsource (subcooled confuser of the nozzle) and, finally, show that the process\nof nucleation of nanoclusters inside a source is of heterogeneous nature. The\nwidth of the silver nanocluster jet (of mass 1024 atoms) reaching target\naccording to sumulations, is in good agreement with that obtained in the\nexperiment coating profile on the target substrate in a form of narrow strip\nmade of stainless steel, that further validates the numerical simulations.", "category": "cond-mat_other" }, { "text": "Fundamental dissipation due to bound fermions in the zero-temperature\n limit: The ground state of a fermionic condensate is well protected against\nperturbations in the presence of an isotropic gap. Regions of gap suppression,\nsurfaces and vortex cores which host Andreev-bound states, seemingly lift that\nstrict protection. Here we show that the role of bound states is more subtle:\nwhen a macroscopic object moves in superfluid $^3$He at velocities exceeding\nthe Landau critical velocity, little to no bulk pair breaking takes place,\nwhile the damping observed originates from the bound states covering the moving\nobject. We identify two separate timescales that govern the bound state\ndynamics, one of them much longer than theoretically anticipated, and show that\nthe bound states do not interact with bulk excitations.", "category": "cond-mat_other" }, { "text": "Effect of the Zero-Mode on the Response of a Trapped Bose-Condensed Gas: The dynamical response of a trapped Bose-Einstein condensate (BEC) is\nformulated consistently with quantum field theory and is numerically evaluated.\nWe regard the BEC as a manifestation of the breaking of the global phase\nsymmetry. Then, the Goldstone theorem implies the existence of a zero energy\nexcitation mode (the zero-mode). We calculate the effect of the zero-mode on\nthe response frequency and show that the contribution of the zero-mode to the\nfirst excitation mode is not so important in the parameter set realized in the\nexisting experiment. This is the reason that experimental results can be\ndescribed using the Bogoliubov prescription, although it breaks the consistency\nof the description in quantum field theory.", "category": "cond-mat_other" }, { "text": "Nucleation of helium in liquid lithium: Fusion energy stands out as a promising alternative for a future decarbonised\nenergy system. To be sustainable, future fusion nuclear reactors will have to\nproduce their own tritium. In the so-called breeding blanket of a reactor, the\nneutron bombardment of lithium will produce the desired tritium, but also\nhelium, which can trigger nucleation mechanisms owing to the very low\nsolubility of helium in liquid metals. An understanding of the underlying\nmicroscopic processes is important for improving the efficiency, sustainability\nand reliability of the fusion energy conversion process. A spontaneous creation\nof helium drops or bubbles in the liquid metal used as breeding material in\nsome designs may be a serious issue for the performance of the breeding\nblankets. This phenomenon has yet to be fully studied and understood. This work\naims to provide some insight on the behavior of lithium and helium mixtures at\nexperimentally corresponding operating conditions (843 K and pressures between\n0.1 and 7 GPa). We report a microscopic study of the thermodynamic, structural\nand dynamical properties of lithium-helium mixtures, as a first step to the\nsimulation of the environment in a nuclear fusion power plant. We introduce a\nmicroscopic model devised to describe the formation of helium drops in the\nthermodynamic range considered. A transition from a miscible homogeneous\nmixture to a phase-separated one, in which helium drops are nucleated, is\nobserved as the pressure is increased above 0.175 GPa. The diffusion\ncoefficient of lithium (2 {\\AA} 2 /ps) is in excellent agreement with reference\nexperimental data, whereas the diffusion coefficient of helium is in the range\nof 1 {\\AA} 2 /ps and tends to decrease as pressure increases. The radii of\nhelium drops have been found to be between 1 and 2 {\\AA}.", "category": "cond-mat_other" }, { "text": "Quantum Ratchets at High Temperatures: Using the continued-fraction method we solve the Caldeira-Leggett master\nequation in the phase-space (Wigner) representation to study Quantum ratchets.\nBroken spatial symmetry, irreversibility and periodic forcing allows for a net\ncurrent in these systems. We calculate this current as a function of the force\nunder adiabatic conditions. Starting from the classical limit we make the\nsystem quantal. In the quantum regime tunnel events and over-barrier wave\nreflection phenomena modify the classical result. Finally, using the\nphase-space formalism we give some insights about the decoherence in these\nsystems.", "category": "cond-mat_other" }, { "text": "Three-dimensional character of atom-chip-based rf-dressed potentials: We experimentally investigate the properties of radio-frequency-dressed\npotentials for Bose-Einstein condensates on atom chips. The three-dimensional\npotential forms a connected pair of parallel waveguides. We show that\nrf-dressed potentials are robust against the effect of small magnetic-field\nvariations on the trap potential. Long-lived dipole oscillations of condensates\ninduced in the rf-dressed potentials can be tuned to a remarkably low damping\nrate. We study a beam-splitter for Bose-Einstein condensates and show that a\npropagating condensate can be dynamically split in two vertically separated\nparts and guided along two paths. The effect of gravity on the potential can be\ntuned and compensated for using a rf-field gradient.", "category": "cond-mat_other" }, { "text": "Quench dynamics and non equilibrium phase diagram of the Bose-Hubbard\n model: We investigate the time evolution of correlations in the Bose-Hubbard model\nfollowing a quench from the superfluid to the Mott insulating phase. For large\nvalues of the final interaction strength the system approaches a distinctly\nnon-equilibrium steady state that bears strong memory of the initial\nconditions. In contrast, when the final interaction strength is comparable to\nthe hopping, the correlations are rather well approximated by those at thermal\nequilibrium. The existence of two distinct non-equilibrium regimes is\nsurprising given the non-integrability of the Bose-Hubbard model. We relate\nthis phenomena to the role of quasi-particle interactions in the Mott\ninsulating state.", "category": "cond-mat_other" }, { "text": "Static Electric Field in a 1D Systems without Boundaries: In this brief report, we show that in a 1D system with unit-cell doubling,\nthe coefficient of the $\\theta$-term is not only determined the topological\nindex, $\\int i\\bra{u_k}\\frac{\\d}{\\d k}\\ket{u_k}{\\rm d}k$. Specifically, the\nrelative position between the electronic orbitals and the ions also alters the\ncoefficient. This resolves a paradox when we apply our previous result to the\nSu-Shreiffer-Heeger model where the two ground states related by a lattice\ntranslation have $\\theta$ differed by $\\pi$. We also show that the static\ndielectric screening is the same with or without boundaries, on the contrary to\nwhat we have commented in our previous paper.", "category": "cond-mat_other" }, { "text": "The Kelvin-wave cascade in the vortex filament model: The energy transfer mechanism in zero temperature superfluid turbulence of\nhelium-4 is still a widely debated topic. Currently, the main hypothesis is\nthat weakly nonlinear interacting Kelvin waves transfer energy to sufficiently\nsmall scales such that energy is dissipated as heat via phonon excitations.\nTheoretically, there are at least two proposed theories for Kelvin-wave\ninteractions. We perform the most comprehensive numerical simulation of weakly\nnonlinear interacting Kelvin-waves to date and show, using a specially designed\nnumerical algorithm incorporating the full Biot-Savart equation, that our\nresults are consistent with nonlocal six-wave Kelvin wave interactions as\nproposed by L'vov and Nazarenko.", "category": "cond-mat_other" }, { "text": "Polarization fine-structure and enhanced single-photon emission of\n self-assembled lateral InGaAs quantum dot molecules embedded in a planar\n micro-cavity: Single lateral InGaAs quantum dot molecules have been embedded in a planar\nmicro-cavity in order to increase the luminescence extraction efficiency. Using\na combination of metal-organic vapor phase and molecular beam epitaxy samples\ncould be produced that exhibit a 30 times enhanced single-photon emission rate.\nWe also show that the single-photon emission is fully switchable between two\ndifferent molecular excitonic recombination energies by applying a lateral\nelectric field. Furthermore, the presence of a polarization fine-structure\nsplitting of the molecular neutral excitonic states is reported which leads to\ntwo polarization-split classically correlated biexciton exciton cascades. The\nfine-structure splitting is found to be on the order of 10 micro-eV.", "category": "cond-mat_other" }, { "text": "Correlations in Ultracold Trapped Few-Boson Systems: Transition from\n Condensation to Fermionization: We study the correlation properties of the ground states of few ultracold\nbosons, trapped in double wells of varying barrier height in one dimension.\nExtending previous results on the signature of the transition from a\nBose-condensed state via fragmentation to the hard-core limit, we provide a\ndeeper understanding of that transition by relating it to the loss of coherence\nin the one-body density matrix and to the emerging long-range tail in the\nmomentum spectrum. These are accounted for in detail by discussing the natural\norbitals and their occupations. Our discussion is complemented by an analysis\nof the two-body correlation function.", "category": "cond-mat_other" }, { "text": "Shape dynamics during deposit of simple metal clusters on rare gas\n matrices: Using a combined quantum mechanical/classical method, we study the collisions\nof small Na clusters on large Ar clusters as a model for cluster deposit. We\nwork out basic mechanisms by systematic variation of collision energy, system\nsizes, and orientations. The soft Ar material is found to serve as an extremely\nefficient shock absorber. The collisional energy is quickly transfered at first\nimpact and the Na clusters are always captured by the Ar surface. The\ndistribution of the collision energy into the Ar system proceeds very fast with\nvelocity of sound. The relaxation of shapes goes at a slower pace using times\nof several ps. It produces a substantial rearrangement of the Ar system while\nthe Na cluster remains rather robust.", "category": "cond-mat_other" }, { "text": "Adiabatic Connection in the Low-Density Limit: In density functional theory (DFT), the exchange-correlation functional can\nbe exactly expressed by the adiabatic connection integral. It has been noticed\nthat as lambda goes to infinity, the lambda^(-1) term in the expansion of\nW(lambda) vanishes. We provide a simple but rigorous derivation to this exact\ncondition in this work. We propose a simple parametric form for the integrand,\nsatisfying this condition, and show that it is highly accurate for\nweakly-correlated two-electron systems.", "category": "cond-mat_other" }, { "text": "Sodium Bose-Einstein Condensates in an Optical Lattice: The phase transition from a superfluid to a Mott insulator has been observed\nin a $^{23}$Na Bose-Einstein condensate. A dye laser detuned $\\approx 5$nm red\nof the Na $3^2$S$ \\to 3^2$P$_{1/2}$ transition was used to form the three\ndimensional optical lattice. The heating effects of the small detuning as well\nas the three-body decay processes constrained the timescale of the experiment.\nCertain lattice detunings were found to induce a large loss of atoms. These\nloss features were shown to be due to photoassociation of atoms to vibrational\nlevels in the Na$_2$ $(1) ^3\\Sigma_g^+$ state.", "category": "cond-mat_other" }, { "text": "High intermodulation gain in a micromechanical Duffing resonator: In this work we use a micromechanical resonator to experimentally study small\nsignal amplification near the onset of Duffing bistability. The device consists\nof a PdAu beam serving as a micromechanical resonator excited by an adjacent\ngate electrode. A large pump signal drives the resonator near the onset of\nbistability, enabling amplification of small signals in a narrow bandwidth. To\nfirst order, the amplification is inversely proportional to the frequency\ndifference between the pump and signal. We estimate the gain to be about 15dB\nfor our device.", "category": "cond-mat_other" }, { "text": "Extreme times in financial markets: We apply the theory of continuous time random walks to study some aspects of\nthe extreme value problem applied to financial time series. We focus our\nattention on extreme times, specifically the mean exit time and the mean\nfirst-passage time. We set the general equations for these extremes and\nevaluate the mean exit time for actual data.", "category": "cond-mat_other" }, { "text": "Dynamics of the vortex line density in superfluid counterflow turbulence: Describing superfluid turbulence at intermediate scales between the\ninter-vortex distance and the macroscale requires an acceptable equation of\nmotion for the density of quantized vortex lines $\\cal{L}$. The closure of such\nan equation for superfluid inhomogeneous flows requires additional inputs\nbesides $\\cal{L}$ and the normal and superfluid velocity fields. In this paper\nwe offer a minimal closure using one additional anisotropy parameter $I_{l0}$.\nUsing the example of counterflow superfluid turbulence we derive two coupled\nclosure equations for the vortex line density and the anisotropy parameter\n$I_{l0}$ with an input of the normal and superfluid velocity fields. The\nvarious closure assumptions and the predictions of the resulting theory are\ntested against numerical simulations.", "category": "cond-mat_other" }, { "text": "Non-equilibrium dynamics of a Bose-Einstein condensate in an optical\n lattice: The dynamical evolution of a Bose-Einstein condensate trapped in a\none-dimensional lattice potential is investigated theoretically in the\nframework of the Bose-Hubbard model. The emphasis is set on the\nfar-from-equilibrium evolution in a case where the gas is strongly interacting.\nThis is realized by an appropriate choice of the parameters in the Hamiltonian,\nand by starting with an initial state, where one lattice well contains a\nBose-Einstein condensate while all other wells are empty. Oscillations of the\ncondensate as well as non-condensate fractions of the gas between the different\nsites of the lattice are found to be damped as a consequence of the collisional\ninteractions between the atoms. Functional integral techniques involving\nself-consistently determined mean fields as well as two-point correlation\nfunctions are used to derive the two-particle-irreducible (2PI) effective\naction. The action is expanded in inverse powers of the number of field\ncomponents N, and the dynamic equations are derived from it to next-to-leading\norder in this expansion. This approach reaches considerably beyond the\nHartree-Fock-Bogoliubov mean-field theory, and its results are compared to the\nexact quantum dynamics obtained by A.M. Rey et al., Phys. Rev. A 69, 033610\n(2004) for small atom numbers.", "category": "cond-mat_other" }, { "text": "Bound states of attractive Bose-Einstein condensates in shallow traps in\n two and three dimensions: Using variational and numerical solutions of the mean-field Gross-Pitaevskii\nequation for attractive interaction (with cubic or Kerr nonlinearity) we show\nthat a stable bound state can appear in a Bose-Einstein condensate (BEC) in a\nlocalized exponentially-screened radially-symmetric harmonic potential well in\ntwo and three dimensions. We also consider an axially-symmetric configuration\nwith zero axial trap and a exponentially-screened radial trap so that the\nresulting bound state can freely move along the axial direction like a soliton.\nThe binding of the present states in shallow wells is mostly due to the\nnonlinear interaction with the trap playing a minor role. Hence these BEC\nstates are more suitable to study the effect of the nonlinear force on the\ndynamics. We illustrate the highly nonlinear nature of breathing oscillation of\nthese states. Such bound states could be created in BECs and studied in the\nlaboratory with present knowhow.", "category": "cond-mat_other" }, { "text": "Stationary waves in a supersonic flow of a two-component Bose gas: A stationary wave pattern occurring in a flow of a two-component\nBose-Einstein condensate past an obstacle is studied. We consider the general\ncase of unequal velocities of two superfluid components. The Landau criterium\napplied to the two-component system determines a certain region in the velocity\nspace in which superfluidity may take place. Stationary waves arise out of this\nregion, but under the additional condition that the relative velocity of the\ncomponents does not exceed some critical value. Under increase of the relative\nvelocity the spectrum of the excitations becomes complex valued and the\nstationary wave pattern is broken. In case of equal velocities two sets of\nstationary waves that correspond to the lower and the upper Bogolyubov mode can\narise. If one component flows and the other is at rest only one set of waves\nmay emerge. Two or even three interfere sets of waves may arise if the\nvelocities approximately of equal value and the angle between the velocities is\nclose to pi/2. In two latter cases the stationary waves correspond to the lower\nmode and the densities of the components oscillate out-of-phase. The ratio of\namplitudes of the components in the stationary waves is computed. This quantity\ndepends on the relative velocity, is different for different sets of waves, and\nvaries along the crests of the waves. For the cases where two or three waves\ninterfere the density images are obtained.", "category": "cond-mat_other" }, { "text": "Quantum Monte Carlo study of ring-shaped polariton parametric\n luminescence in a semiconductor microcavity: We present a quantum Monte Carlo study of the quantum correlations in the\nparametric luminescence from semiconductor microcavities in the strong\nexciton-photon coupling regime. As already demonstrated in recent experiments,\na ring-shaped emission is obtained by applying two identical pump beams with\nopposite in-plane wavevectors, providing symmetrical signal and idler beams\nwith opposite in-plane wavevectors on the ring. We study the squeezing of the\nsignal-idler difference noise across the parametric instability threshold,\naccounting for the radiative and non-radiative losses, multiple scattering and\nstatic disorder. We compare the results of the complete multimode Monte Carlo\nsimulations with a simplified linearized quantum Langevin analytical model.", "category": "cond-mat_other" }, { "text": "Bose-Einstein condensate in a quartic potential: Static and Dynamic\n properties: In this paper, we present a theoretical study of a Bose-Einstein condensate\nof interacting bosons in a quartic trap in one, two, and three dimensions.\nUsing Thomas-Fermi approximation, suitably complemented by numerical solutions\nof the Gross-Pitaevskii equation, we study the ground sate condensate density\nprofiles, the chemical potential, the effects of cross-terms in the quartic\npotential, temporal evolution of various energy components of the condensate,\nand width oscillations of the condensate. Results obtained are compared with\ncorresponding results for a bose condensate in a harmonic confinement.", "category": "cond-mat_other" }, { "text": "Potential energy threshold for nano-hillock formation by impact of slow\n highly charged ions on a CaF$_2$(111) surface: We investigate the formation of nano-sized hillocks on the (111) surface of\nCaF$_2$ single crystals by impact of slow highly charged ions. Atomic force\nmicroscopy reveals a surprisingly sharp and well-defined threshold of potential\nenergy carried into the collision of about 14 keV for hillock formation.\nEstimates of the energy density deposited suggest that the threshold is linked\nto a solid-liquid phase transition (``melting'') on the nanoscale. With\nincreasing potential energy, both the basal diameter and the height of the\nhillocks increase. The present results reveal a remarkable similarity between\nthe present predominantly potential-energy driven process and track formation\nby the thermal spike of swift ($\\sim$ GeV) heavy ions.", "category": "cond-mat_other" }, { "text": "Nanoelectromechanical systems based on multi-walled nanotubes:\n nanothermometer, nanorelay and nanoactuator: We report on three new types of nanoelectromechanical systems based on carbon\nnanotubes: an electromechanical nanothermometer, a nanorelay and a nanomotor.\nThe nanothermometer can be used for accurate temperature measurements in\nspatially localized regions with dimensions of several hundred nanometers. The\nnanorelay is a prototype of a memory cell, and the nanoactuator can be used for\ntransformation of the forward force into the relative rotation of the walls.\nRelative motion of the walls in these nanosystems is defined by the shape of\nthe interwall interaction energy surface. Ab initio and semi-empirical\ncalculations have been used to estimate the operational characteristics and\ndimensions of these nanosystems.", "category": "cond-mat_other" }, { "text": "Thomas-Fermi Screening in Graphene: The in-plane static screening of the field originated by a charge placed in a\ngraphene sheet is investigated. A self-consistent field equation in the real\nspace domain is obtained by using a suitable Thomas-Fermi procedure. Exact and\napproximated (for qualitative considerations) solutions are presented. In the\ncase of a charged sheet, the screened potential presents a tail dependent on\nthe free carrier density whose importance is connected with the local features\nof the impurity system. Early conclusions about Thomas-Fermi screening in\ngraphene are revised.", "category": "cond-mat_other" }, { "text": "Exciton Spin Dynamics in Semiconductor Quantum Wells: In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum\nWells. The spin properties of excitons in nanostructures are determined by\ntheir fine structure. We will mainly focus in this review on GaAs and InGaAs\nquantum wells which are model systems.", "category": "cond-mat_other" }, { "text": "Nonlinear Electrokinetics at large applied voltages: The classical theory of electrokinetic phenomena assumes a dilute solution of\npoint-like ions in chemical equilibrium with a surface whose double-layer\nvoltage is of order the thermal voltage, $k_BT/e = 25$ mV. In nonlinear\n``induced-charge'' electrokinetic phenomena, such as AC electro-osmosis,\nseveral Volts $\\approx 100 k_BT/e$ are applied to the double layer, so the\ntheory breaks down and cannot explain many observed features. We argue that,\nunder such a large voltage, counterions ``condense'' near the surface, even for\ndilute bulk solutions. Based on simple models, we predict that the double-layer\ncapacitance decreases and the electro-osmotic mobility saturates at large\nvoltages, due to steric repulsion and increased viscosity of the condensed\nlayer, respectively. The former suffices to explain observed high frequency\nflow reversal in AC electro-osmosis; the latter leads to a salt concentration\ndependence of induced-charge flows comparable to experiments, although a\ncomplete theory is still lacking.", "category": "cond-mat_other" }, { "text": "Numerical observation of Hawking radiation from acoustic black holes in\n atomic Bose-Einstein condensates: We report numerical evidence of Hawking emission of Bogoliubov phonons from a\nsonic horizon in a flowing one-dimensional atomic Bose-Einstein condensate. The\npresence of Hawking radiation is revealed from peculiar long-range patterns in\nthe density-density correlation function of the gas. Quantitative agreement\nbetween our fully microscopic calculations and the prediction of analog models\nis obtained in the hydrodynamic limit. New features are predicted and the\nrobustness of the Hawking signal against a finite temperature discussed.", "category": "cond-mat_other" }, { "text": "Resonant Dimer Relaxation in Cold Atoms with a Large Scattering Length: Efimov physics refers to universal phenomena associated with a discrete\nscaling symmetry in the 3-body problem with a large scattering length. The\nfirst experimental evidence for Efimov physics was the recent observation of a\nresonant peak in the 3-body recombination rate for 133Cs atoms with large\nnegative scattering length. There can also be resonant peaks in the atom-dimer\nrelaxation rate for large positive scattering length. We calculate the\natom-dimer relaxation rate as a function of temperature and show how\nmeasurements of the relaxation rate can be used to determine accurately the\nparameters that govern Efimov physics.", "category": "cond-mat_other" }, { "text": "Ratchet, pawl and spring Brownian motor: We present a model for a thermal Brownian motor based on Feynman's famous\nratchet and pawl device. Its main feature is that the ratchet and the pawl are\nin different thermal baths and connected by an harmonic spring. We simulate its\ndynamics, explore its main features and also derive an approximate analytical\nsolution for the mean velocity as a function of the external torque applied and\nthe temperatures of the baths. Such theoretical predictions and the results\nfrom numerical simulations agree within the ranges of the approximations\nperformed.", "category": "cond-mat_other" }, { "text": "Quantum phases of hardcore bosons with long-range interactions on a\n square lattice: We study the ground-state phase diagrams of hardcore bosons with long-range\ninteractions on a square lattice using the linear spin-wave theory and a\ncluster mean-field method. Specifically, we consider the two types of\nlong-range interaction: One consists only of the nearest- and\nnext-nearest-neighbor interactions, and the other is the dipole-dipole\ninteraction that decays with the interparticle distance $r$ as $\\sim r^{-3}$.\nIt is known from previous analyses by quantum Monte Carlo methods that a\ncheckerboard supersolid (CSS) is absent in the ground-state phase diagram of\nthe former case while it is present in the latter. In the former, we find that\nquantum fluctuations around mean-field solutions are enhanced by the direct\ncompetition between the checkerboard and striped solid orders and that they\ndestabilize the CSS phase. On the other hand, the emergence of the CSS phase in\nthe latter case can be attributed to the absence of such a competition with\nother solid orders. We also show that the cluster mean-field method allows for\nthe determination of phase boundaries in a precise quantitative manner when\nscaling with respect to the cluster size is taken into account. It is found\nthat the phase transition between the superfluid and the solid (or CSS) is of\nthe first order in the vicinity of the particle-hole symmetric line.", "category": "cond-mat_other" }, { "text": "Density-functional theory of nonequilibrium tunneling: Nanoscale optoelectronics and molecular-electronics systems operate with\ncurrent injection and nonequilibrium tunneling, phenomena that challenge\nconsistent descriptions of the steady-state transport. The current affects the\nelectron-density variation and hence the inter- and intra-molecular bonding\nwhich in turn determines the transport magnitude. The standard approach for\nefficient characterization of steady-state tunneling combines ground-state\ndensity functional theory (DFT) calculations (of an effective scattering\npotential) with a Landauer-type formalism and ignores all actual many-body\nscattering. The standard method also lacks a formal variational basis. This\npaper formulates a Lippmann-Schwinger collision density functional theory\n(LSC-DFT) for tunneling transport with full electron-electron interactions.\nQuantum-kinetic (Dyson) equations are used for an exact reformulation that\nexpresses the variational noninteracting and interacting many-body scattering\nT-matrices in terms of universal density functionals. The many-body\nLippmann-Schwinger (LS) variational principle defines an implicit equation for\nthe exact nonequilibrium density.", "category": "cond-mat_other" }, { "text": "On surface plasmon polariton wavepacket dynamics in metal-dielectric\n heterostructures: The WKB equations for dynamics of the surface plasmon polariton (SPP)\nwavepacket are studied. The dispersion law for the SPP in the metal-dielectric\nheterostructure with varying thickness of a perforated dielectric layer is\nrigorously calculated and investigated using the scattering matrix method. Two\nchannels of the SPP wavepacket optical losses related to the absorption in a\nmetal and to the SPP leakage are analyzed. It is shown that change of the\ndielectric layer thickness acts on the SPP as an external force leading to\nevolution of its quasimomentum and to the wavepacket reversal or even to the\noptical Bloch oscillations (BO). Properties of these phenomena are investigated\nand discussed. Typical values of the BO amplitude are about tens of microns and\nthe period is around tens or hundreds of femtoseconds.", "category": "cond-mat_other" }, { "text": "Electromagnetically induced transparency in an atom-molecule\n Bose-Einstein condensate: We propose a new measurement scheme for the atom-molecule dark state by using\nelectromagnetically induced transparency (EIT) technique. Based on a\ndensity-matrix formalism, we calculate the absorption coefficient numerically.\nThe appearance of the EIT dip in the spectra profile gives clear evidence for\nthe creation of the dark state in the atom-molecule Bose-Einstein condensate.", "category": "cond-mat_other" }, { "text": "A Complex Chemical Potential: Signature of Decay in a Bose-Einstein\n Condensate: We explore the zero-temperature statics of an atomic Bose-Einstein condensate\nin which a Feshbach resonance creates a coupling to a second condensate\ncomponent of quasi-bound molecules. Using a variational procedure to find the\nequation of state, the appearance of this binding is manifest in a collapsing\nground state, where only the molecular condensate is present up to some\ncritical density. Further, an excited state is seen to reproduce the usual\nlow-density atomic condensate behavior in this system, but the molecular\ncomponent is found to produce an underlying decay, quantified by the imaginary\npart of the chemical potential. Most importantly, the unique decay rate\ndependencies on density ($\\sim \\rho ^{3/2}$) and on scattering length ($\\sim\na^{5/2}$) can be measured in experimental tests of this theory.", "category": "cond-mat_other" }, { "text": "Analysis of patterns formed by two-component diffusion limited\n aggregation: We consider diffusion limited aggregation of particles of two different\nkinds. It is assumed that a particle of one kind may adhere only to another\nparticle of the same kind. The particles aggregate on a linear substrate which\nconsists of periodically or randomly placed particles of different kinds. We\nanalyze the influence of initial patterns on the structure of growing clusters.\nIt is shown that at small distances from the substrate, the cluster structures\nrepeat initial patterns. However, starting from a critical distance the initial\nperiodicity is abruptly lost, and the particle distribution tends to a random\none. An approach describing the evolution of the number of branches is\nproposed. Our calculations show that the initial patter can be detected only at\nthe distance which is not larger than approximately one and a half of the\ncharacteristic pattern size.", "category": "cond-mat_other" }, { "text": "Quantization scheme of surface plasma polariton in helical liquid and\n the exchanging interaction between quasi particles and emitters: The collective modes of helical electron gases interacting with light have\nbeen studied in an extended random phase approximation. By separating two kinds\nof electron density oscillations, the complicate operator dynamics coupling\nelectrons and photons can be simplified and solved. The inverse operator\ntransformation that interprets electron oscillations and photons with quasi\nparticles has been developed to study the interaction between surface plasma\npolaritons (SPPs) and emitters. Besides the ordinary interaction induced by\nelectric field, we find an additional term which plays important roles at small\ndistance arising from electron exchanging effect.", "category": "cond-mat_other" }, { "text": "Evidence that rotons in helium II are interstitial atoms: Superfluid helium II contains excitations known as rotons. Their properties\nhave been studied experimentally for more than 70 years but their structure is\nnot fully understood. Feynman's 1954 description, involving rotating flow\npatterns, does not fully explain later experimental data. Here we identify\nvolumetric, thermodynamic, colloidal, excitation, x-ray and neutron scattering\nevidence that rotons are composed of interstitial helium atoms. We show in\nparticular that they have the same mass, effective mass and activation energy\nwithin experimental accuracy. They readily move through the substrate, and\ncouple through lattice vibrations to produce quantized, loss-free flow which\ncorresponds to the observed superflow. Our observations revive London's 1936\nconclusion that helium II has a relatively open crystal-like lattice with\nenough free volume for atoms to move relative to one another, and reconcile it\nwith London's 1938 description of a quantum fluid.", "category": "cond-mat_other" }, { "text": "Combining high pressure and coherent diffraction: a first feasibility\n test: We present a first experiment combining high pression and coherent X-ray\ndiffraction. By using a dedicated diamond anvil cell, we show that the degree\nof coherence of the X-ray beam is preserved when the X-ray beam passes through\nthe diamond cell. This observation opens the possibility of studying the\ndynamics of slow fluctuations under high pressure.", "category": "cond-mat_other" }, { "text": "Crossover in Broad Feshbach Resonance with Energy-Dependent Coupling: This paper has been withdrawn by the authors as the recent measurement of the\nclosed channel population for Li6 [Partridge et al., cond-mat/0505353]\nindicates that the cutoff energy is still much larger than any other relevant\nenergy scales for this broad Feshbach resonance.", "category": "cond-mat_other" }, { "text": "Bipartite Yule Processes in Collections of Journal Papers: Collections of journal papers, often referred to as 'citation networks', can\nbe modeled as a collection of coupled bipartite networks which tend to exhibit\nlinear growth and preferential attachment as papers are added to the\ncollection. Assuming primary nodes in the first partition and secondary nodes\nin the second partition, the basic bipartite Yule process assumes that as each\nprimary node is added to the network, it links to multiple secondary nodes, and\nwith probability, $\\alpha$, each new link may connect to a newly appearing\nsecondary node. The number of links from a new primary node follows some\ndistribution that is a characteristic of the specific network. Links to\nexisting secondary nodes follow a preferential attachment rule. With\nmodifications to adapt to specific networks, bipartite Yule processes simulate\nnetworks that can be validated against actual networks using a wide variety of\nnetwork metrics. The application of bipartite Yule processes to the simulation\nof paper-reference networks and paper-author networks is demonstrated and\nsimulation results are shown to mimic networks from actual collections of\npapers across several network metrics.", "category": "cond-mat_other" }, { "text": "Structural Study of Adsorbed Helium Films: New Approach with Synchrotron\n Radiation X-rays: A few atomic layers of helium adsorbed on graphite have been attracting much\nattention as one of the ideal quantum systems in two dimension. Although\nprevious reports on neutron diffraction have shown fundamental structural\ninformation in these systems, there still remain many open questions. Here, we\npropose surface crystal truncation rod (CTR) scatterings using synchrotron\nradiation X-rays as a promising method to reveal surface and interface\nstructures of helium films on graphite at temperatures below 2 K, based on the\npreliminary experimental results on a monolayer of He-4 on a thin graphite. Our\nestimation on heat generation by X-ray irradiations also suggests that CTR\nscatterings are applicable to even at system temperatures near 100 mK.", "category": "cond-mat_other" }, { "text": "Kolmogorov spectrum of superfluid turbulence: numerical analysis of the\n Gross-Pitaevskii equation with the small scale dissipation: The energy spectrum of superfluid turbulence is studied numerically by\nsolving the Gross-Pitaevskii equation. We introduce the dissipation term which\nworks only in the scale smaller than the healing length, to remove short\nwavelength excitations which may hinder the cascade process of quantized\nvortices in the inertial range. The obtained energy spectrum is consistent with\nthe Kolmogorov law.", "category": "cond-mat_other" }, { "text": "Spectroscopy, upconversion dynamics, and applications of Er3+-doped\n low-phonon materials: In this work I summarize some of the recent work carried out by our group on\nthe upconversion dynamics of Er3+-doped potassium lead halide crystals, which\npossess very small phonons and present very efficient blue and green\nupconversion. Furthermore, a non-conventional application of these RE-doped\nlow-phonon materials in optical refrigeration of luminescent solids is also\ndiscussed, paying especial attention to new pathways for optical cooling that\ninclude infrared-to-visible upconversion. Finally, I conclude with some hints\nof what I think it is the next step into improving the luminescence efficiency\nof solids: the use of RE-doped nanoscale photonic heterostructures for\ncontrolling the density of photonic states.", "category": "cond-mat_other" }, { "text": "Digital Processing in Tunneling Spectroscopy: An alternative approach to detect very weak singularities on the\ncharacteristics of a tunnel diode is proposed in which the numerical\ndifferential filtering is applied directly to measured current versus voltage\ndependence instead of the modulation technique commonly used with this purpose.\nThe gains and looses of the both approaches in the particular case of tunneling\ninvestigations of semiconductors under pressure are discussed. The\ncorresponding circuitry and mathematical routines are presented.", "category": "cond-mat_other" }, { "text": "Phonon-Induced Quantum Magnetic Deflagration in Mn12: A comprehensive set of experiments on the effect of high-frequency surface\nacoustic waves, SAWs, in the spin relaxation in Mn12-acetate is presented. We\nhave studied the quantum magnetic deflagration induced by SAWs under various\nexperimental conditions extending the data shown in a very recent paper [A.\nHernandez-Minguez et. al., Phys. Rev. Lett. 95, 217205 (2005)]. We have focused\nour study on the dependence of both the ignition time and the propagation speed\nof the magnetic avalanches on the frequency, amplitude, and duration of the SAW\npulses in experiments performed under different temperatures and external\nmagnetic fields.", "category": "cond-mat_other" }, { "text": "A strongly interacting Bose gas: Nozi\u00e8res and Schmitt-Rink theory and\n beyond: We calculate the critical temperature for Bose-Einstein condensation in a gas\nof bosonic atoms across a Feshbach resonance, and show how medium effects at\nnegative scattering lengths give rise to pairs reminiscent of the ones\nresponsible for fermionic superfluidity. We find that the formation of pairs\nleads to a large suppression of the critical temperature. Within the formalism\ndeveloped by Nozieres and Schmitt-Rink the gas appears mechanically stable\nthroughout the entire crossover region, but when interactions between pairs are\ntaken into account we show that the gas becomes unstable close to the critical\ntemperature. We discuss prospects of observing these effects in a gas of\nultracold Cs133 atoms where recent measurements indicate that the gas may be\nsufficiently long-lived to explore the many-body physics around a Feshbach\nresonance.", "category": "cond-mat_other" }, { "text": "Distortion of the Stoner-Wohlfarth astroid by a spin-polarized current: The Stoner-Wohlfarth astroid is a fundamental object in magnetism. It\nseparates regions of the magnetic field space with two stable magnetization\nequilibria from those with only one stable equilibrium and it characterizes the\nmagnetization reversal of nano-magnets induced by applied magnetic fields. On\nthe other hand, it was recently demonstrated that transfer of spin angular\nmomentum from a spin-polarized current provides an alternative way of switching\nthe magnetization. Here, we examine the astroid of a nano-magnet with uniaxial\nmagnetic anisotropy under the combined influence of applied fields and\nspin-transfer torques. We find that spin-transfer is most efficient at\nmodifying the astroid when the external field is applied along the easy-axis of\nmagnetization. On departing from this situation, a threshold current appears\nbelow which spin-transfer becomes ineffective yielding a current-induced dip in\nthe astroid along the easy-axis direction. An extension of the Stoner-Wohlfarth\nmodel is outlined which accounts for this phenomenon.", "category": "cond-mat_other" }, { "text": "Phase Space Wannier Functions in Electronic Structure Calculations: We consider the applicability of phase space Wannier functions\" to electronic\nstructure calculations. These generalized Wannier functions are analogous to\nlocalized plane waves and constitute a complete, orthonormal set which is\nexponentially localized both in position and momentum space. Their properties\nare described and an illustrative application to bound states in one dimension\nis presented. Criteria for choosing basis set size and lattice constant are\ndiscussed based on semi-classical, phase space considerations. Convergence of\nthe ground state energy with respect to basis size is evaluated. Comparison\nwith plane-waves basis sets indicates that the number of phase space Wannier\nfunctions needed for convergence can be signicantly smaller in three\ndimensions. PACS: 71.10.+x, 71.50.+t", "category": "cond-mat_other" }, { "text": "Adiabatic quenches through an extended quantum critical region: By gradually changing the degree of the anisotropy in a XXZ chain we study\nthe defect formation in a quantum system that crosses an extended critical\nregion. We discuss two qualitatively different cases of quenches, from the\nantiferromagnetic to the ferromagnetic phase and from the critical to the\nantiferromegnetic phase. By means of time-dependent DMRG simulations, we\ncalculate the residual energy at the end of the quench as a characteristic\nquantity gauging the loss of adiabaticity. We find the dynamical scalings of\nthe residual energy for both types of quenches, and compare them with the\npredictions of the Kibble-Zurek and Landau-Zener theories.", "category": "cond-mat_other" }, { "text": "Barrier crossing to the small Holstein polaron regime: We investigate the dimensionality effects of the Holstein polaron from the\nfully quantum regime, where the crossover between large and small polaron\nsolutions is known to be continuous in all dimensions, into the limit described\nby the semiclassical Discrete Nonlinear Schr\\\"odinger (DNLS) Equation, where\nthe crossover is continuous in 1D but discontinuous in higher dimensions. We\nuse exact numerics on one hand and a two variable parametrization of the\nToyozawa ansatz on the other in order to probe the crossover region in all\nparameter regimes. We find that a barrier appears also in 1D separating the two\ntypes of solutions, seemingly in contradiction to the common paradigm for the\nDNLS according to which the crossover is barrier-free. We quantify the polaron\nbehavior in the crossover region as a function of the exciton overlap and find\nthat the barrier remains small in 1D and tunnelling through it is not\nrate-limiting.", "category": "cond-mat_other" }, { "text": "Simulating hyperbolic space on a circuit board: The Laplace operator encodes the behavior of physical systems at vastly\ndifferent scales, describing heat flow, fluids, as well as electric,\ngravitational, and quantum fields. A key input for the Laplace equation is the\ncurvature of space. Here we discuss and experimentally demonstrate that the\nspectral ordering of Laplacian eigenstates for hyperbolic (negatively curved)\nand flat two-dimensional spaces has a universally different structure. We use a\nlattice regularization of hyperbolic space in an electric-circuit network to\nmeasure the eigenstates of a \"hyperbolic drum\", and in a time-resolved\nexperiment we verify signal propagation along the curved geodesics. Our\nexperiments showcase both a versatile platform to emulate hyperbolic lattices\nin tabletop experiments, and a set of methods to verify the effective\nhyperbolic metric in this and other platforms. The presented techniques can be\nutilized to explore novel aspects of both classical and quantum dynamics in\nnegatively curved spaces, and to realise the emerging models of topological\nhyperbolic matter.", "category": "cond-mat_other" }, { "text": "Quantum Monte-Carlo study of a two-species boson Hubbard model: We consider a two-species hard-core boson Hubbard model for a supersolid,\nwhere the two types of bosons represent vacancies and interstitials doped into\na commensurate crystal. The on-site inter-species interaction may create bound\nstates of vacancies and interstitials facilitating vacancy condensation at\nlower energies than in a single-species model, as suggested in an earlier mean\nfield study. Here we carry out quantum Monte Carlo simulation to study possible\nsupersolid phases of the model, corresponding to superfluid phases of the\nvacancies or interstitials. At low temperatures, we find three distinct\nsuperfluid phases. The extent of the phases and the nature of the phase\ntransitions are discussed in comparison to mean-field theory.", "category": "cond-mat_other" }, { "text": "From a nonlinear string to a weakly interacting Bose gas: We investigate a real scalar field whose dynamics is governed by a nonlinear\nwave equation. We show that classical description can be applied to a quantum\nsystem of many interacting bosons provided that some quantum ingredients are\nincluded. An universal action has to be introduced in order to define particle\nnumber. The value of this action should be equal to the Planck constant. This\nconstrain can be imposed by removing high frequency modes from the dynamics by\nintroducing a cut-off. We show that the position of the cut-off has to be\ncarefully adjusted. Finally, we show the proper choice of the cut-off ensures\nthat all low frequency eigenenmodes which are taken into account are\nmacroscopically occupied.", "category": "cond-mat_other" }, { "text": "Magnetic levitation induced by negative permeability: In this paper we study the interaction between a point magnetic dipole and a\nsemi-infinite metamaterial using the method of images. We obtain analytical\nexpressions for the levitation force for an arbitrarily oriented dipole.\nSurprisingly the maximal levitation force for negative permeability is found to\nbe stronger compared to the case when the dipole is above a superconductor.", "category": "cond-mat_other" }, { "text": "Ground state of two electrons on concentric spheres: We extend our analysis of two electrons on a sphere [Phys. Rev. A {\\bf 79},\n062517 (2009); Phys. Rev. Lett. {\\bf 103}, 123008 (2009)] to electrons on\nconcentric spheres with different radii. The strengths and weaknesses of\nseveral electronic structure models are analyzed, ranging from the mean-field\napproximation (restricted and unrestricted Hartree-Fock solutions) to\nconfiguration interaction expansion, leading to near-exact wave functions and\nenergies. The M{\\o}ller-Plesset energy corrections (up to third-order) and the\nasymptotic expansion for the large-spheres regime are also considered. We also\nstudy the position intracules derived from approximate and exact wave\nfunctions. We find evidence for the existence of a long-range Coulomb hole in\nthe large-spheres regime, and infer that unrestricted Hartree-Fock theory\nover-localizes the electrons.", "category": "cond-mat_other" }, { "text": "Magnetization and specific heat of TbFe3(BO3)4: Experiment and crystal\n field calculations: We have studied the thermodynamic properties of single-crystalline\nTbFe3(BO3)4. Magnetization measurements have been carried out as a function of\nmagnetic field (up to 50 T) and temperature up to 350K with the magnetic field\nboth parallel and perpendicular to the trigonal c-axis of the crystal. The\nspecific heat has been measured in the temperature range 2-300K with a magnetic\nfield up to 9 T applied parallel to the c-axis. The data indicate a structural\nphase transition at 192 K and antiferromagnetic spin ordering at 40 K. A\nSchottky anomaly is present in the specific heat data around 20 K, arising due\nto two low-lying energy levels of the Tb3+ ions being split by f-d coupling.\nBelow TN magnetic fields parallel to the c-axis drive a spin-flop phase\ntransition, which is associated with a large magnetization jump. The highly\nanisotropic character of the magnetic susceptibility is ascribed mainly to the\nIsing-like behavior of the Tb3+ ions in the trigonal crystal field. We describe\nour results in the framework of an unified approach which is based on\nmean-field approximation and crystal-field calculations.", "category": "cond-mat_other" }, { "text": "Correlation effects on the static structure factor of a Bose gas: A theoretical treatment of the static structure factor $S(k)$ of a Bose gas\nis attempted. The low order expansion theory is implemented for the\nconstruction of the two body density distribution, while various trial\nfunctions for the radial distribution function $g(r)$ are used. $g(r)$\nintroduces the atomic correlations and describes the departure from the\nnoninteracting gas. The Bose gas is studied as inhomogeneous one, trapped in\nharmonic oscillator well, as well as homogeneous. A suitable parametrization of\nthe various trial functions $g(r)$ exists which leads to satisfactory\nreproduction of the experimental values of $S(k)$, both in inhomogeneous case\nas well as in homogeneous one. The phonon range behavior of the calculated\n$S(k)$ is also addressed and discussed both in finite and infinite Bose gas.", "category": "cond-mat_other" }, { "text": "Study of the Magnetic Film Materials by Horizontal Scanning Mode for the\n Magnetic Force Microscopy in Magnetostatic and ac Regimes: The magnetic force microscopy inverse problem for the case of horizontal\nscanning of a tip on a linear magnetic film is introduced. We show the\npossibility to recover the magnetic permeability of the material from the\nexperimental data by using the Hankel (Fourier-Bessel) transform inverse method\n(HIM). This method is applied to the case of a layered slab film as well. The\ninverse problem related to the ac MFM is introduced.", "category": "cond-mat_other" }, { "text": "Exciton BCS or BEC state in a semiconductor bilayer system?: We calculate the off-diagonal long range order (ODLRO) terms of the\nexciton--exciton correlation function of a semiconductor bilayer system with\nCoulomb interaction and a transverse magnetic field. We show that the formation\nof a BEC state is very sensitive to the width of the interaction in momentum\nspace. This dependence is analytically derived and represents the key physical\ningredient for the formation (or not) of an exciton condensate state.", "category": "cond-mat_other" }, { "text": "Photoluminescence Spectroscopy of the Molecular Biexciton in Vertically\n Stacked Quantum Dot Pairs: We present photoluminescence studies of the molecular neutral\nbiexciton-exciton spectra of individual vertically stacked InAs/GaAs quantum\ndot pairs. We tune either the hole or the electron levels of the two dots into\ntunneling resonances. The spectra are described well within a few-level,\nfew-particle molecular model. Their properties can be modified broadly by an\nelectric field and by structural design, which makes them highly attractive for\ncontrolling nonlinear optical properties.", "category": "cond-mat_other" }, { "text": "Conversion Efficiencies of Heteronuclear Feshbach Molecules: We study the conversion efficiency of heteronuclear Feshbach molecules in\npopulation imbalanced atomic gases formed by ramping the magnetic field\nadiabatically. We extend the recent work [J. E. Williams et al., New J. Phys.,\n8, 150 (2006)] on the theory of Feshbach molecule formations to various\ncombinations of quantum statistics of each atomic component. A simple\ncalculation for a harmonically trapped ideal gas is in good agreement with the\nrecent experiment [S. B. Papp and C. E. Wieman, Phys. Rev. Lett., 97, 180404\n(2006)] without any fitting parameters. We also give the conversion efficiency\nas an explicit function of initial peak phase space density of the majority\nspecies for population imbalanced gases. In the low-density region where\nBose-Einstein condensation does not appear, the conversion efficiency is a\nmonotonic function of the initial peak phase space density, but independent of\nstatistics of a minority component. The quantum statistics of majority atoms\nhas a significant effect on the conversion efficiency. In addition,\nBose-Einstein condensation of an atomic component is the key element\ndetermining the maximum conversion efficiency.", "category": "cond-mat_other" }, { "text": "Frustration of Decoherence in Open Quantum Systems: We study a model of frustration of decoherence in an open quantum system.\nContrary to other dissipative ohmic impurity models, such as the Kondo model or\nthe dissipative two-level system, the impurity model discussed here never\npresents overdamped dynamics even for strong coupling to the environment. We\nshow that this unusual effect has its origins in the quantum mechanical nature\nof the coupling between the quantum impurity and the environment. We study the\nproblem using analytic and numerical renormalization group methods and obtain\nexpressions for the frequency and temperature dependence of the impurity\nsusceptibility in different regimes.", "category": "cond-mat_other" }, { "text": "Floquet system, Bloch oscillation, and Stark ladder: We prove the multi-band Bloch oscillation and Stark ladder in the $nk$ and\nsite representation from the Floquet theorem. The proof is also possible from\nthe equivalence between the Floquet system, Bloch oscillation, and the rotator\nwith spin. We also exactly solve the periodically driven two level atom and two\nband Bloch oscillation in terms of Heun function.", "category": "cond-mat_other" }, { "text": "Precise determination of $^6$Li cold collision parameters by\n radio-frequency spectroscopy on weakly bound molecules: We employ radio-frequency spectroscopy on weakly bound $^6$Li$_2$ molecules\nto precisely determine the molecular binding energies and the energy splittings\nbetween molecular states for different magnetic fields. These measurements\nallow us to extract the interaction parameters of ultracold $^6$Li atoms based\non a multi-channel quantum scattering model. We determine the singlet and\ntriplet scattering lengths to be $a_s=45.167(8)a_0$ and $a_t=-2140(18)a_0$ (1\n$a_0$ = 0.0529177 nm), and the positions of the broad Feshbach resonances in\nthe energetically lowest three $s-$wave scattering channels to be 83.41(15) mT,\n69.04(5) mT, and 81.12(10) mT.", "category": "cond-mat_other" }, { "text": "Spin dynamics triggered by sub-terahertz magnetic field pulses: Current pulses of up to 20 A and as short as 3 ps are generated by a low\ntemperature grown GaAs (lt-GaAs) photoconductive switch and guided through a\ncoplanar waveguide, resulting in a 0.6 Tesla terahertz (THz) magnetic field\npulse. The pulse length is directly calibrated using photocurrent\nautocorrelation. Magnetic excitations in Fe microstructures are studied by\ntime-resolved Kerr spectroscopy and compared with micromagnetic simulations. A\nresponse within less than 10 ps to the THz electromagnetic field pulse is\nfound.", "category": "cond-mat_other" }, { "text": "The Dynamic Structure Factor of the 1D Bose Gas near the Tonks-Girardeau\n Limit: While the 1D Bose gas appears to exhibit superfluid response under certain\nconditions, it fails the Landau criterion according to the elementary\nexcitation spectrum calculated by Lieb. The apparent riddle is solved by\ncalculating the dynamic structure factor of the Lieb-Liniger 1D Bose gas. A\npseudopotential Hamiltonian in the fermionic representation is used to derive a\nHartree-Fock operator, which turns out to be well-behaved and local. The\nRandom-Phase approximation for the dynamic structure factor based on this\nderivation is calculated analytically and is expected to be valid at least up\nto first order in $1/\\gamma$, where $\\gamma$ is the dimensionless interaction\nstrength of the model. The dynamic structure factor in this approximation\nclearly indicates a crossover behavior from the non-superfluid Tonks to the\nsuperfluid weakly-interacting regime, which should be observable by Bragg\nscattering in current experiments.", "category": "cond-mat_other" }, { "text": "The Ginzburg-Landau model of Bose-Einstein condensation of magnons: We introduce a system of phenomenological equations for Bose-Einstein\ncondensates of magnons in the one-dimensional setting. The nonlinearly coupled\nequations, written for amplitudes of the right-and left-traveling waves,\ncombine basic features of the Gross-Pitaevskii and complex Ginzburg-Landau\nmodels. They include localized source terms, to represent the microwave\nmagnon-pumping field. With the source represented by the $\\delta $-functions,\nwe find analytical solutions for symmetric localized states of the magnon\ncondensates. We also predict the existence of asymmetric states with unequal\namplitudes of the two components. Numerical simulations demonstrate that all\nanalytically found solutions are stable. With the $\\delta $-function terms\nreplaced by broader sources, the simulations reveal a transition from the\nsingle-peak stationary symmetric states to multi-peak ones, generated by the\nmodulational instability of extended nonlinear-wave patterns. In the\nsimulations, symmetric initial conditions always converge to symmetric\nstationary patterns. On the other hand, asymmetric inputs may generate\nnonstationary asymmetric localized solutions, in the form of traveling or\nstanding waves. Comparison with experimental results demonstrates that the\nphenomenological equations provide for a reasonably good model for the\ndescription of the spatiotemporal dynamics of magnon condensates.", "category": "cond-mat_other" }, { "text": "Fermions at unitarity and Haldane Exclusion Statistics: We consider a gas of neutral fermionic atoms at ultra-low temperatures, with\nthe attractive interaction tuned to Feshbach resonance. We calculate, the\nvariation of the chemical potential and the energy per particle as a function\nof temperature by assuming the system to be an ideal gas obeying the Haldane-Wu\nfractional exclusion statistics. Our results for the untrapped gas compare\nfavourably with the recently published Monte Carlo calculations of two groups.\nFor a harmonically trapped gas, the results agree with experiment, and also\nwith other published work.", "category": "cond-mat_other" }, { "text": "A Simple Experimental Setup for Simultaneous Superfluid-response and\n Heat-capacity Measurements for Helium in Confined Geometries: Torsional oscillator (TO) is an experimental technique which is widely used\nto investigate superfluid responses in helium systems confined in porous\nmaterials or adsorbed on substrates. In these systems, heat capacity (HC) is\nalso an important quantity to study the local thermodynamic properties. We have\ndeveloped a simple method to incorporate the capability of HC measurement into\nan existing TO without modifying the TO itself. By inserting a rigid thermal\nisolation support made of alumina and a weak thermal link made of fine copper\nwires between a standard TO and the mixing chamber of a dilution refrigerator\nin parallel, we were able to carry out simultaneous TO and HC measurements on\nexactly the same helium sample, i.e., four atomic layers of $^4$He adsorbed on\ngraphite, with good accuracies down to 30 mK. The data reproduced very well the\nprevious workers' results obtained independently using setups optimized for\nindividual measurements. This method is conveniently applicable to a variety of\nexperiments where careful comparisons between results of TO and HC measurements\nare crucial. We describe how to design the thermal isolation support and the\nweak thermal link to manage conflicting requirements in the two techniques.", "category": "cond-mat_other" }, { "text": "Examining electron-boson coupling using time-resolved spectroscopy: Nonequilibrium pump-probe time domain spectroscopies can become an important\ntool to disentangle degrees of freedom whose coupling leads to broad structures\nin the frequency domain. Here, using the time-resolved solution of a model\nphotoexcited electron-phonon system we show that the relaxational dynamics are\ndirectly governed by the equilibrium self-energy so that the phonon frequency\nsets a window for \"slow\" versus \"fast\" recovery. The overall temporal structure\nof this relaxation spectroscopy allows for a reliable and quantitative\nextraction of the electron-phonon coupling strength without requiring an\neffective temperature model or making strong assumptions about the underlying\nbare electronic band dispersion.", "category": "cond-mat_other" }, { "text": "Scaling law for seismic hazard after a main shock: After a large earthquake, the likelihood of successive strong aftershocks\nneeds to be estimated. Exploiting similarities with critical phenomena, we\nintroduce a scaling law for the decay in time following a main shock of the\nexpected number of aftershocks greater than a certain magnitude. Empirical\nresults that support our scaling hypothesis are obtained from analyzing the\nrecord of earthquakes in California. The proposed form unifies the well-known\nOmori and Gutenberg-Richter laws of seismicity, together with other\nphenomenological observations. Our results substantially modify presently\nemployed estimates and may lead to an improved assessment of seismic hazard\nafter a large earthquake.}", "category": "cond-mat_other" }, { "text": "Artificial electromagnetism for neutral atoms: Escher staircase and\n Laughlin liquids: We show how lasers may create fields which couple to neutral atoms in the\nsame way that the electromagnetic fields couple to charged particles. These\nfields are needed for using neutral atoms as an analog quantum computer for\nsimulating the properties of many-body systems of charged particles. They allow\nfor seemingly paradoxical geometries, such as a ring where atoms continuously\nreduce their potential energy while moving in a closed path. We propose neutral\natom experiments which probe quantum Hall effects and the interplay between\nmagnetic fields and periodic potentials.", "category": "cond-mat_other" }, { "text": "Potential and charge-carrier concentration distributions in solid\n electrolyte between flat electrodes: Statistically studied are the equilibrium characteristics of a subsystem of\nmobile charges of one sort, taking into account the subsystem of fixed charges\nof the opposite sign creating a compensating electric background. The\ndistribution of these charges under the influence of the external field is\ninvariable. To represent free energy of the subsystem of mobile charges in the\nform of a functional of their density and to calculate cell potentials of the\nmean forces by the method of conditional distributions, a cumulant expansion\nwith respect to the renormalized Mayer functions is used. To take into account\nthe screening effects, the results of the collective variables method are used.\nA system of integral equations for the potentials of mean forces is obtained\nthat accounts for the effects of near- and long-range interactions. The\ncalculations are made in the lattice approximation. The correlation component\ndistinguished in the expression for the binary distribution function makes it\npossible to calculate the correlated and uncorrelated parts of the electric\npotential using the Poisson equation. In the case of sufficiently small\nelectric fields, a linear expansion of the chemical potential in terms of\ndeviation of the charge concentration from the homogeneous distribution is\nconsidered. In final calculations the correlation between particles is taken\ninto account in the approximation of the first neighbors. In this approximation\nthe potential and charge concentration distribution is described by a linear\ndifferential equation of the fourth order. The results of its analytical\nsolution and subsequent numerical calculations for the characteristics of solid\nelectrolyte are analyzed.", "category": "cond-mat_other" }, { "text": "Reptation quantum Monte Carlo for lattice Hamiltonians with a\n directed-update scheme: We provide an extension to lattice systems of the reptation quantum Monte\nCarlo algorithm, originally devised for continuous Hamiltonians. For systems\naffected by the sign problem, a method to systematically improve upon the\nso-called fixed-node approximation is also proposed. The generality of the\nmethod, which also takes advantage of a canonical worm algorithm scheme to\nmeasure off-diagonal observables, makes it applicable to a vast variety of\nquantum systems and eases the study of their ground-state and excited-states\nproperties. As a case study, we investigate the quantum dynamics of the\none-dimensional Heisenberg model and we provide accurate estimates of the\nground-state energy of the two-dimensional fermionic Hubbard model.", "category": "cond-mat_other" }, { "text": "Proximity Effects in Radiative Transfer: Though the dependence of near-field radiative transfer on the gap between two\nplanar objects is well understood, that between curved objects is still\nunclear. We show, based on the analysis of the surface polariton mediated\nradiative transfer between two spheres of equal radii $R$ and minimum gap $d$,\nthat the near--field radiative transfer scales as $R/d$ as $d/R \\rightarrow 0$\nand as $\\ln(R/d)$ for larger values of $d/R$ up to the far--field limit. We\npropose a modified form of the proximity approximation to predict near--field\nradiative transfer between curved objects from simulations of radiative\ntransfer between planar surfaces.", "category": "cond-mat_other" }, { "text": "Manifestations of the Efimov Effect for Three Identical Bosons: In this paper we present results from numerical calculations for three\nidentical boson systems for both very large and infinite two-body s-wave\nscattering length $a$. We have considered scattering lengths up to $2\\times\n10^5$ a.u. and solved the hyperangular part of the Schr\\\"odinger equation for\ndistances up to $10^6$ a.u.. Form these, we obtained the three-body effective\npotentials, hyperspherical channel functions and the asymptotic behavior of the\nnonadiabatic couplings in order to to characterize the main aspects of the\nEfimov states. These results allow us to test and quantify the assumptions\nrelated to the Efimov effect.", "category": "cond-mat_other" }, { "text": "Breeding and Solitary Wave Behavior of Dunes: Beautiful dune patterns can be found in deserts and along coasts due to the\ninstability of a plain sheet of sand under the action of the wind. Barchan\ndunes are highly mobile aeolian dunes found in areas of low sand availability\nand unidirectional wind fields. Up to now modelization mainly focussed on\nsingle dunes or dune patterns without regarding the mechanisms of dune\ninteractions. We study the case when a small dune bumps into a bigger one.\nRecently Schwammle et al. and Katsuki et al. have shown that under certain\ncircumstances dunes can behave like solitary waves. This means that they can\n``cross'' each other which has been questioned by many researchers before. In\nother cases we observe coalescence, i.e. both dune merge into one, breeding,\ni.e. the creation of three baby dunes at the center and horns of a Barchan, or\nbudding, i.e. the small dune, after ``crossing'' the big one, is unstable and\nsplits into two new dunes.", "category": "cond-mat_other" }, { "text": "Slit-array transmission loss feasibility in airborne sound: Recent experiments conducted in water at ultrasonic frequencies showed the\npossibility of overcoming the transmission loss provided by homogeneous plates\nat certain frequencies by drilling periodically distributed holes on it. In\nthis letter, the feasibility of using slit arrays to increase the transmission\nloss at certain frequencies for airborne sound is studied. Numerical results\npredict a) very low transmission loss for a slit array in comparison with a\nhomogeneous plate in air and b) the transmission loss of a slit array can\novercome that of a homogeneous plate if the impedance mismatch is low enough.", "category": "cond-mat_other" }, { "text": "Spin-correlation functions in ultracold paired atomic-fermion systems:\n sum rules, self-consistent approximations, and mean fields: The spin response functions measured in multi-component fermion gases by\nmeans of rf transitions between hyperfine states are strongly constrained by\nthe symmetry of the interatomic interactions. Such constraints are reflected in\nthe spin f-sum rule that the response functions must obey. In particular, only\nif the effective interactions are not fully invariant in SU(2) spin space, are\nthe response functions sensitive to mean field and pairing effects. We\ndemonstrate, via a self-consistent calculation of the spin-spin correlation\nfunction within the framework of Hartree-Fock-BCS theory, how one can derive a\ncorrelation function explicitly obeying the f-sum rule. By contrast, simple\none-loop approximations to the spin response functions do not satisfy the sum\nrule. As we show, the emergence of a second peak at higher frequency in the rf\nspectrum, as observed in a recent experiment in trapped $^6\\text{Li}$, can be\nunderstood as the contribution from the paired fermions, with a shift of the\npeak from the normal particle response proportional to the square of the BCS\npairing gap.", "category": "cond-mat_other" }, { "text": "Quasimodes of a chaotic elastic cavity with increasing local losses: We report non-invasive measurements of the complex field of elastic\nquasimodes of a silicon wafer with chaotic shape. The amplitude and phase\nspatial distribution of the flexural modes are directly obtained by Fourier\ntransform of time measurements. We investigate the crossover from real mode to\ncomplex-valued quasimode, when absorption is progressively increased on one\nedge of the wafer. The complexness parameter, which characterizes the degree to\nwhich a resonance state is complex-valued, is measured for non-overlapping\nresonances and is found to be proportional to the non-homogeneous contribution\nto the line broadening of the resonance. A simple two-level model based on the\neffective Hamiltonian formalism supports our experimental results.", "category": "cond-mat_other" }, { "text": "Ultrafast optical Faraday effect in transparent solids: We predict a strong-field ultrafast optical Faraday effect, where a\ncircularly polarized ultrashort optical pulse induces transient chirality in an\nachiral transparent dielectric. This effect is attractive for time-resolved\nmeasurements because it gives access to the non-instantaneity of the nonlinear\nmedium response, and also because it represents relaxation of time-reversal\nsymmetry by all-optical means. We propose probing the induced transient\nchirality with a weak linearly polarized ultraviolet pulse that is shorter than\nthe near-infrared pump pulse. The predicted effects are ultrafast: the induced\nchirality vanishes for probe delays exceeding the duration of the near-infrared\npulse. This opens up possibilities for applications in ultrafast\ncircular-polarization modulators and analyzers.", "category": "cond-mat_other" }, { "text": "Finite-Temperature Behavior of an Inter-species Fermionic Superfluid\n with Population Imbalance: We determine the superfluid transition temperature $T_c$ and related finite\ntemperature phase diagrams for the entire BCS-Bose Einstein condensation\ncrossover in a homogeneous mixture of $^{6}$Li and $^{40}$K atoms with\npopulation imbalance. Our work is motivated by the recent observation of an\ninter-species Feshbach resonance. Pairing fluctuation effects, which\nsignificantly reduce $T_c$ from the onset temperature for pairing ($T^*$),\nprovide reasonable estimates of $T_c$ and indicate that the inter-species\nsuperfluid phase should be accessible in future experiments. Although a\ngeneralized-Sarma phase is not stable in the ground state near unitarity, our\nphase diagrams show that it appears as an intermediate-temperature superfluid.", "category": "cond-mat_other" }, { "text": "Effective single-particle order-N scheme for the dynamics of open\n non-interacting many-body systems: Quantum master equations are common tools to describe the dynamics of\nmany-body systems open to an environment. Due to the interaction with the\nlatter, even for the case of non-interacting electrons, the computational cost\nto solve these equations increases exponentially with the particle number. We\npropose a simple scheme, that allows to study the dynamics of $N$\nnon-interacting electrons taking into account both dissipation effects and\nFermi statistics, with a computational cost that scales linearly with $N$. Our\nmethod is based on a mapping of the many-body system to a specific set of\neffective single-particle systems. We provide detailed numerical results\nshowing excellent agreement between the effective single-particle scheme and\nthe exact many-body one, as obtained from studying the dynamics of two\ndifferent systems. In the first, we study optically-induced currents in quantum\nrings at zero temperature, and in the second we study a linear chain coupled at\nits ends to two thermal baths with different (finite) temperatures. In\naddition, we give an analytical justification for our method, based on an exact\naveraging over the many-body states of the original master equations.", "category": "cond-mat_other" }, { "text": "Theory of vortex-lattice melting in a one-dimensional optical lattice: We investigate quantum and temperature fluctuations of a vortex lattice in a\none-dimensional optical lattice. We discuss in particular the Bloch bands of\nthe Tkachenko modes and calculate the correlation function of the vortex\npositions along the direction of the optical lattice. Because of the small\nnumber of particles in the pancake Bose-Einstein condensates at every site of\nthe optical lattice, finite-size effects become very important. Moreover, the\nfluctuations in the vortex positions are inhomogeneous due to the inhomogeneous\ndensity. As a result, the melting of the lattice occurs from the outside\ninwards. However, tunneling between neighboring pancakes substantially reduces\nthe inhomogeneity as well as the size of the fluctuations. On the other hand,\nnonzero temperatures increase the size of the fluctuations dramatically. We\ncalculate the crossover temperature from quantum melting to classical melting.\nWe also investigate melting in the presence of a quartic radial potential,\nwhere a liquid can form in the center instead of at the outer edge of the\npancake Bose-Einstein condensates.", "category": "cond-mat_other" }, { "text": "A generalised Landau-Lifshitz equation for isotropic SU(3) magnet: In the paper we obtain equations for large-scale fluctuations of the mean\nfield (the field of magnetization and quadrupole moments) in a magnetic system\nrealized by a square (cubic) lattice of atoms with spin s >= 1 at each site. We\nuse the generalized Heisenberg Hamiltonian with biquadratic exchange as a\nquantum model. A quantum thermodynamical averaging gives classical effective\nmodels, which are interpreted as Hamiltonian systems on coadjoint orbits of Lie\ngroup SU(3).", "category": "cond-mat_other" }, { "text": "Magneto and ferroelectric phase transitions in HoMn2O5 monocrystals: From the physical point of view multiferroics present an extremely\ninteresting class of systems and problems. These are essentially of two kinds.\nOne is what are the microscopic conditions, and sometimes constrains, which\ndetermine the possibility to combine in one system both magnetic and\nferroelectric properties. This turned out to be a quite nontrivial question,\nand usually, in conventional systems, these two phenomena tend to exclude one\nanother. Why it is the case is an important and still not completely resolved\nissue. In the present article we report our results from magnetic properties\nmeasurements on HoMn2O5 with short discussion about it possible origin.", "category": "cond-mat_other" }, { "text": "Density-density functionals and effective potentials in many-body\n electronic structure calculations: We demonstrate the existence of different density-density functionals\ndesigned to retain selected properties of the many-body ground state in a\nnon-interacting solution starting from the standard density functional theory\nground state. We focus on diffusion quantum Monte Carlo applications that\nrequire trial wave functions with optimal Fermion nodes. The theory is\nextensible and can be used to understand current practices in several\nelectronic structure methods within a generalized density functional framework.\nThe theory justifies and stimulates the search of optimal empirical density\nfunctionals and effective potentials for accurate calculations of the\nproperties of real materials, but also cautions on the limits of their\napplicability. The concepts are tested and validated with a near-analytic\nmodel.", "category": "cond-mat_other" }, { "text": "Coherent Destruction of Photon Emission from a Single Molecule Source: A\n Renormalization Group Approach: The photon emission from a single molecule driven simultaneously by a laser\nand a slow electric radio frequency (rf) field is studied. We use a\nnon-Hermitian Hamiltonian approach which accounts for the radiative decay of a\ntwo level system modeling a single molecule source. We apply the\nrenormalization group method for differential equations to obtain long time\nsolution of the corresponding Schrdinger equation, which allows us to calculate\nthe average waiting time for the first photon emission. Then, we analyze the\nconditions for suppression and enhancement of photon emission in this\ndissipative two-level system. In particular we derive a transcendental\nequation, which yields the non-trivial rf field control parameters, for which\nenhancement and suppression of photon emission occurs. For finite values of\nradiative decay rate an abrupt transition from the molecule's localization in\nits ground state to delocalization is found for certain critical values of the\nrf field parameters. Our results are shown to be in agreement with the\navailable experiments [Ch. Brunel et al, Phys. Rev. Lett. 81, 2679 (1998)].", "category": "cond-mat_other" }, { "text": "Coherent Control of Rydberg States in Silicon: We demonstrate coherent control of donor wavefunctions in phosphorous-doped\nsilicon. Our experiments take advantage of a free electron laser to stimulate\nand observe photon echoes from, and Rabi oscillations between the ground and\nfirst excited state of P donors in Si.", "category": "cond-mat_other" }, { "text": "Comparison study of DFA and DMA methods in analysis of autocorrelations\n in time series: Statistics of the Hurst scaling exponents calculated with the use of two\nmethods: recently introduced Detrended Moving Average Analysis(DMA) and\nDetrended Fluctuation Analysis (DFA)are compared. Analysis is done for\nartificial stochastic Brownian time series of various length and reveals\ninteresting statistical relationships between two methods. Good agreement\nbetween DFA and DMA techniques is found for long time series $L\\sim 10^{5}$,\nhowever for shorter series we observe that two methods give different results\nwith no systematic relation between them. It is shown that, on the average, DMA\nmethod overestimates the Hurst exponent comparing it with DFA technique.", "category": "cond-mat_other" }, { "text": "Photoacoustic ultrasound sources from diffusion-limited aggregates: Metallic diffusion-limited aggregate (DLA) films are well-known to exhibit\nnear-perfect broadband optical absorption. We demonstrate that such films also\nmanifest a substantial and relatively material-independent photoacoustic\nresponse, as a consequence of their random nanostructure. We theoretically and\nexperimentally analyze photoacoustic phenomena in DLA films, and show that they\ncan be used to create broadband air- coupled acoustic sources. These sources\nare inexpensive and simple to fabricate, and work into the ultrasonic regime.\nWe illustrate the device possibilities by building and testing an\noptically-addressed acoustic phased array capable of producing virtually\narbitrary acoustic intensity patterns in air.", "category": "cond-mat_other" }, { "text": "Anomalous quantum mass flow of atoms in p-wave resonance: I analyze an atomic Fermi gas with a planar p-wave interaction, motivated by\nthe experimentally observed anisotropy in p-wave Feshbach resonances. An axial\nsuperfluid state is verified. A domain wall object is discovered to be a new\ntopological defect of this superfluid and an explicit solution has been found.\nGapless quasiparticles appear as bound states on the wall, dispersing in the\nspace of reduced dimensions. Surprisingly, they are chiral, deeply related to\nfermion zero modes and anomalies in quantum chromodynamics. The chirality of\nthe superfluid is manifested by a persistent anomalous mass current of atoms in\nthe groundstate. This spectacular quantum phenomenon is a prediction for future\nexperiments.", "category": "cond-mat_other" }, { "text": "Yukawa bosons in two-dimensional Harmonic confinement: The ground state property of Yukawa Bose fluid confined in a radial harmonic\ntrap is studied. The calculation was carried out using the density functional\ntheory formalism within the Kohn-Sham scheme. The excess-correlation energy for\nthis inhomogeneous fluid is approximated via the local density approximation. A\ncomparison is also made with the Gross-Piteavskii model. We found that the\nsystem of bosons interacting in terms of Yukawa potential in a harmonic trap is\nenergetically favorable compared to the ones interacting via contact delta\npotential.", "category": "cond-mat_other" }, { "text": "Inverse Borrmann effect in photonic crystals: The Borrmann effect, which is related to the microscopic distribution of the\nelectromagnetic field inside the primitive cell, is studied in photonic and\nmagnetophotonic crystals. This effect, well-known in x-ray spectroscopy, is\nresponsible for the enhancement or suppression of various linear and nonlinear\noptical effects when the incidence angle and/or the frequency change. It is\nshown that by design of the primitive cell this effect can be suppressed and\neven inverted.", "category": "cond-mat_other" }, { "text": "Theory of Magnetodynamics Induced by Spin Torque in Perpendicularly\n Magnetized Thin Films: A nonlinear model of spin wave excitation using a point contact in a thin\nferromagnetic film is introduced. Large-amplitude magnetic solitary waves are\ncomputed, which help explain recent spin-torque experiments. Numerical\nsimulations of the fully nonlinear model predict excitation frequencies in\nexcess of 0.2 THz for contact diameters smaller than 6 nm. Simulations also\npredict a saturation and red shift of the frequency at currents large enough to\ninvert the magnetization under the point contact. The theory is approximated by\na cubic complex Ginzburg-Landau type equation. The mode's nonlinear frequency\nshift is found by use of perturbation techniques, whose results agree with\nthose of direct numerical simulations.", "category": "cond-mat_other" }, { "text": "Magnetic vortices induced by a moving tip: A two-dimensional easy-plane ferromagnetic substrate, interacting with a\ndipolar tip which is magnetised perpendicular with respect to the easy plane is\nstudied numerically by solving the Landau-Lifshitz Gilbert equation. Due to the\nsymmetry of the dipolar field of the tip, in addition to the collinear\nstructure a magnetic vortex structure becomes stable. It is robust against\nexcitations caused by the motion of the tip. We show that for high excitations\nthe system may perform a transition between the two states. The influence of\ndomain walls, which may also induce this transition, is examined.", "category": "cond-mat_other" }, { "text": "Harmonic oscillator model for current- and field-driven magnetic\n vortices: In experiments the distinction between spin-torque and Oersted-field driven\nmagnetization dynamics is still an open problem. Here, the gyroscopic motion of\ncurrent- and field-driven magnetic vortices in small thin-film elements is\ninvestigated by analytical calculations and by numerical simulations. It is\nfound that for small harmonic excitations the vortex core performs an\nelliptical rotation around its equilibrium position. The global phase of the\nrotation and the ratio between the semi-axes are determined by the frequency\nand the amplitude of the Oersted field and the spin torque.", "category": "cond-mat_other" }, { "text": "Simulating hyperbolic space on a circuit board: The Laplace operator encodes the behavior of physical systems at vastly\ndifferent scales, describing heat flow, fluids, as well as electric,\ngravitational, and quantum fields. A key input for the Laplace equation is the\ncurvature of space. Here we discuss and experimentally demonstrate that the\nspectral ordering of Laplacian eigenstates for hyperbolic (negatively curved)\nand flat two-dimensional spaces has a universally different structure. We use a\nlattice regularization of hyperbolic space in an electric-circuit network to\nmeasure the eigenstates of a \"hyperbolic drum\", and in a time-resolved\nexperiment we verify signal propagation along the curved geodesics. Our\nexperiments showcase both a versatile platform to emulate hyperbolic lattices\nin tabletop experiments, and a set of methods to verify the effective\nhyperbolic metric in this and other platforms. The presented techniques can be\nutilized to explore novel aspects of both classical and quantum dynamics in\nnegatively curved spaces, and to realise the emerging models of topological\nhyperbolic matter.", "category": "cond-mat_other" }, { "text": "Fluctuation spectroscopy of surface melting of ice without, and with\n impurities: Water, in its three phases, is ubiquitous, and the surface properties of ice\nis important to clarifying the process of melting, as well as to various other\nfields, including geophysics. As such, the subject has been studied both\ntheoretically and experimentally, for over a hundred years, while being an\nactive field of research today. It has been established that surface melting,\nor premelting, exists below the melting point, and a `liquid-like layer' (LLL)\nexists on the surface of ice. Here, we use the surface thermal fluctuation\nspectra to study the properties of LLL, including its thickness, for pure ice,\nand for ice with impurities. We find that the properties of LLL are consistent\nwith those of bulk liquid water, and for layers thicker than 10\\,nm, their\nproperties are experimentally indistinguishable from those of liquid water.\nMeasured thicknesses are found to be much smaller than the previous\nexperimental measurements close to the bulk melting temperature. We find that\nthe additions of impurities at ppm levels cause LLL to be thicker, as well to\nbe quite inhomogeneous, with properties depending on the dopant. This is\nrevealed by scanning the surface at $\\mu$m level resolution, and can contribute\nto the slipperiness of ice in natural settings.", "category": "cond-mat_other" }, { "text": "Intense slow beams of bosonic potassium isotopes: We report on an experimental realization of a two-dimensional magneto-optical\ntrap (2D-MOT) that allows the generation of cold atomic beams of 39K and 41K\nbosonic potassium isotopes. The high measured fluxes up to 1.0x10^11 atoms/s\nand low atomic velocities around 33 m/s are well suited for a fast and reliable\n3D-MOT loading, a basilar feature for new generation experiments on\nBose-Einstein condensation of dilute atomic samples. We also present a simple\nmultilevel theoretical model for the calculation of the light-induced force\nacting on an atom moving in a MOT. The model gives a good agreement between\npredicted and measured flux and velocity values for our 2D-MOT.", "category": "cond-mat_other" }, { "text": "Collective excitations of trapped Fermi or Bose gases: A new method is developed to calculate all excitations of trapped gases using\nhydrodynamics at zero temperature for any equation of state $\\mu=\\mu(n)$ and\nfor any trapping potential. It is shown that a natural scalar product can be\ndefined for the mode functions, by which the wave operator is hermitian and the\nmode functions are orthogonal. It is also shown that the Kohn-modes are exact\nfor harmonic trapping in hydrodynamic theory. Excitations for fermions are\ncalculated in the BCS-BEC transition region using the equation of state of the\nmean-field Leggett-model for isotrop harmonic trap potential.", "category": "cond-mat_other" }, { "text": "Detecting the tunneling rates for strongly interacting fermions on\n optical lattices: Strongly interacting fermionic atoms on optical lattices are studied through\na Hubbard-like model Hamiltonian, in which tunneling rates of atoms and\nmolecules between neighboring sites are assumed to be different. In the limit\nof large onsite repulsion U, the model is shown to reproduce the t-J\nHamiltonian, in which the J coefficient of the Heisenberg term depends on the\nparticle-assisted tunneling rate g: explicitly, $J=4 g^2/U$. At half-filling, g\ndrives a crossover from a Brinkman-Rice paramagnetic insulator of fully\nlocalized atoms (g=0) to the antiferromagnetic Mott insulator of the standard\nHubbard case (g=t). This is observed already at the intermediate coupling\nregime in the number of doubly occupied sites, thus providing a criterion to\nextract from measurements the effective value of g.", "category": "cond-mat_other" }, { "text": "Disordered Supersolids in the Extended Bose-Hubbard Model: The extended Bose-Hubbard model captures the essential properties of a wide\nvariety of physical systems including ultracold atoms and molecules in optical\nlattices, Josephson junction arrays, and certain narrow band superconductors.\nIt exhibits a rich phase diagram including a supersolid phase where a lattice\nsolid coexists with a superfluid. We use quantum Monte Carlo to study the\nsupersolid part of the phase diagram of the extended Bose-Hubbard model on the\nsimple cubic lattice. We add disorder to the extended Bose-Hubbard model and\nfind that the maximum critical temperature for the supersolid phase tends to be\nsuppressed by disorder. But we also find a narrow parameter window in which the\nsupersolid critical temperature is enhanced by disorder. Our results show that\nsupersolids survive a moderate amount of spatial disorder and thermal\nfluctuations in the simple cubic lattice.", "category": "cond-mat_other" }, { "text": "Vortex shedding from a microsphere oscillating in superfluid ^4He at mK\n temperatures and from a laser beam moving in a Bose-Einstein condensate: Turbulent drag of an oscillating microsphere, that is levitating in\nsuperfluid $^4$He at mK temperatures, is unstable slightly above a critical\nvelocity amplitude $v_c$. The lifetime $\\tau$ of the turbulent state is\ndetermined by the number $n$ of vortices shed per half-period. It is found that\nthis number is identical to the superfluid Reynolds number. The possibility of\nmoving a levitating sphere through superfluid $^3$He at microkelvin\ntemperatures is considered. A laser beam moving through a Bose-Einstein\ncondensate (BEC) (as observed by other authors) also produces vortices in the\nBEC. In particular, in either case a linear dependence of the shedding\nfrequency $f_v$ on $\\Delta v = v - v_c$ is observed, where $v$ is the velocity\namplitude of the sphere or the constant velocity of the laser beam above $v_c$\nfor the onset of turbulent flow: $f_v = a \\Delta v$, where the coefficient $a$\nis proportional to the oscillation frequency $ \\omega $ above some\ncharacteristic frequency $\\omega_k$ and assumes a finite value for steady\nmotion $\\omega \\rightarrow 0$. A relation between the superfluid Reynolds\nnumber and the superfluid Strouhal number is presented that is different from\nclassical turbulence.", "category": "cond-mat_other" }, { "text": "Ultrafast amplification and non-linear magneto-elastic coupling of\n coherent magnon modes in an antiferromagnet: We investigate the role of domain walls in the ultrafast magnon dynamics of\nan antiferromagnetic NiO single crystal in a pump-probe experiment with\nvariable pump photon energy. Analysing the amplitude of the energy-dependent\nphoto-induced ultrafast spin dynamics, we detect a yet unreported coupling\nbetween the material's characteristic THz- and a GHz-magnon modes. We explain\nthis unexpected coupling between two orthogonal eigenstates of the\ncorresponding Hamiltonian by modelling the magneto-elastic interaction between\nspins in different domains. We find that such interaction, in the non-linear\nregime, couples the two different magnon modes via the domain walls and it can\nbe optically exploited via the exciton-magnon resonance.", "category": "cond-mat_other" }, { "text": "Quasiclassical frustration: We study the dissipative properties of a harmonic oscillator subject to two\nindependent heat baths, one of which couples to its position and the other one\nto its momentum. This model describes a large spin impurity in a ferromagnet.\nWe find that some effects of the two heat baths partially cancel each other.\nMost notably, oscillations may remain underdamped for arbitrarily strong\ncoupling. This effect is a direct consequence of the mutually conjugate\ncharacter of position and momentum. For a single dissipative bath coupled\nlinearly to both position and momentum, no underdamped regime is possible for\nstrong coupling. The dynamics of purity loss for one and two wave packets is\nalso investigated.", "category": "cond-mat_other" }, { "text": "Fermion mediated long-range interactions of bosons in the 1D\n Bose-Fermi-Hubbard model: The ground-state phase diagram of mixtures of spin polarized fermions and\nbosons in a 1D periodic lattice is discussed in the limit of large fermion\nhopping and half filling of the fermions. Numerical simulations performed with\nthe density matrix renormalization group (DMRG) show besides bosonic Mott\ninsulating (MI), superfluid (SF), and charge density-wave phases (CDW) a novel\nphase with spatial separation of MI and CDW regions. We derive an effective\nbosonic theory which allows for a complete understanding and quantitative\nprediction of the bosonic phase diagram. In particular the origin of CDW phase\nand the MI-CDW phase separation is revealed as the interplay between\nfermion-induced mean-field potential and long range interaction with\nalternating sign.", "category": "cond-mat_other" }, { "text": "Old wine in new bottles: Onsager's reciprocity relations for the coefficients of transport equations\nare now 87 years old. Sometimes these relations are called the Fourth Law of\nThermodynamics. Among others they provide an effective criterion for the\nexistence of local equilibrium and of microscopic reversibility. Since the\nbeginning of the century Onsager's relations have seen a revival in the field\nof spincaloritronics. There the relations are very helpful in judging the\nutility of modern devices for electronic data processing.", "category": "cond-mat_other" }, { "text": "Infinite average lifetime of an unstable bright state in the green\n fluorescent protein: The time evolution of the fluorescence intensity emitted by well-defined\nensembles of Green Fluorescent Proteins has been studied by using a standard\nconfocal microscope. In contrast with previous results obtained in single\nmolecule experiments, the photo-bleaching of the ensemble is well described by\na model based on Levy statistics. Moreover, this simple theoretical model\nallows us to obtain information about the energy-scales involved in the aging\nprocess.", "category": "cond-mat_other" }, { "text": "Su(3) Algebraic Structure of the Cuprate Superconductors Model based on\n the Analogy with Atomic Nuclei: A cuprate superconductor model based on the analogy with atomic nuclei was\nshown by Iachello to have an $su(3)$ structure. The mean-field approximation\nHamiltonian can be written as a linear function of the generators of $su(3)$\nalgebra. Using algebraic method, we derive the eigenvalues of the reduced\nHamiltonian beyond the subalgebras $u(1)\\bigotimes u(2)$ and $so(3)$ of $su(3)$\nalgebra. In particular, by considering the coherence between s- and d-wave\npairs as perturbation, the effects of coherent term upon the energy spectrum\nare investigated.", "category": "cond-mat_other" }, { "text": "Study of superfluid $^3$He under nanoscale confinement. A new approach\n to the investigation of superfluid $^3$He films: We review recent experiments in which superfluid $^3$He has been studied\nunder highly controlled confinement in nanofluidic sample chambers. We discuss\nthe experimental challenges and their resolution. These methods open the way to\na systematic investigation of the superfluidity of $^3$He films, and the\nsurface and edge excitations of topological superfluids.", "category": "cond-mat_other" }, { "text": "A Computational Study of Rotating Spiral Waves and Spatio-Temporal\n Transient Chaos in a Deterministic Three-Level Active System: Spatio-temporal dynamics of a deterministic three-level cellular automaton\n(TLCA) of Zykov-Mikhailov type (Sov. Phys. - Dokl., 1986, Vol.31, No.1, P.51)\nis studied numerically. Evolution of spatial structures is investigated both\nfor the original Zykov-Mikhailov model (which is applicable to, for example,\nBelousov-Zhabotinskii chemical reactions) and for proposed by us TLCA, which is\na generalization of Zykov-Mikhailov model for the case of two-channel\ndiffusion. Such the TLCA is a minimal model for an excitable medium of\nmicrowave phonon laser, called phaser (D. N. Makovetskii, Tech. Phys., 2004,\nVol.49, No.2, P.224; cond-mat/0402640). The most interesting observed forms of\nTLCA dynamics are as follows: (a) spatio-temporal transient chaos in form of\nhighly bottlenecked collective evolution of excitations by rotating spiral\nwaves (RSW) with variable topological charges; (b) competition of left-handed\nand right-handed RSW with unexpected features, including self-induced\nalteration of integral effective topological charge; (c) transient chimera\nstates, i.e. coexistence of regular and chaotic domains in TLCA patterns; (d)\nbranching of TLCA states with different symmetry which may lead to full\nrestoring of symmetry of imperfect starting pattern. Phenomena (a) and (c) are\ndirectly related to phaser dynamics features observed earlier in real\nexperiments at liquid helium temperatures on corundum crystals doped by\niron-group ions. ACM: F.1.1, I.6, J.2; PACS:05.65.+b, 07.05.Tp, 82.20.Wt", "category": "cond-mat_other" }, { "text": "Dynamical Exchange Interaction From Time-Dependent Spin Density\n Functional Theory: We report on {\\it ab initio} time-dependent spin dynamics simulations for a\ntwo-center magnetic molecular complex based on time-dependent non-collinear\nspin density functional theory. In particular, we discuss how the dynamical\nbehavior of the {\\it ab initio} spin-density in the time-domain can be mapped\nonto a model Hamiltonian based on the classical Heisenberg spin-spin\ninteraction $J\\vcr{S}_1\\cdot \\vcr{S}_2$. By analyzing individual localized-spin\ntrajectories, extracted from the spin-density evolution, we demonstrate a novel\nmethod for evaluating the effective Heisenberg exchange coupling constant, $J$,\nfrom first principles simulations. We find that $J$, extracted in such a new\ndynamical way, agrees quantitatively to that calculated by the standard density\nfunctional theory broken-symmetry scheme.", "category": "cond-mat_other" }, { "text": "Probing pairing gap in Fermi atoms by light scattering: We study stimulated scattering of polarized light in a two-component Fermi\ngas of atoms at zero temperature. Within the framework of Nambu-Gorkov\nformalism, we calculate the response function of superfluid gas taking into\naccount the final state interactions. The dynamic structure factor deduced from\nthe response function provides information about the pairing gap and the\nmomentum distributions of atoms. Model calculations using local density\napproximation indicates that the pairing gap of trapped Fermi gas may be\ndetectable by Bragg spectroscopy due to stimulated scattering.", "category": "cond-mat_other" }, { "text": "Absorbing photonic crystals for thin film photovoltaics: The absorption of thin hydrogenated amorphous silicon layers can be\nefficiently enhanced through a controlled periodic patterning. Light is trapped\nthrough coupling with photonic Bloch modes of the periodic structures, which\nact as an absorbing planar photonic crystal. We theoretically demonstrate this\nabsorption enhancement through one or two dimensional patterning, and show the\nexperimental feasibility through large area holographic patterning. Numerical\nsimulations show over 50% absorption enhancement over the part of the solar\nspectrum comprised between 380 and 750nm. It is experimentally confirmed by\noptical measurements performed on planar photonic crystals fabricated by laser\nholography and reactive ion etching.", "category": "cond-mat_other" }, { "text": "Nonlinear Landau-Zener Processes in a Periodic Driving Field: Effects of a periodic driving field on Landau-Zener processes are studied\nusing a nonlinear two-mode model that describes the mean-field dynamics of a\nmany-body system. A variety of different dynamical phenomena in different\nparameter regimes of the driving field are discussed and analyzed. These\ninclude shifted, weakened, or enhanced phase dependence of nonlinear\nLandau-Zener processes, nonlinearity-enhanced population transfer in the\nadiabatic limit, and Hamiltonian chaos on the mean field level. The emphasis of\nthis work is placed on how the impact of a periodic driving field on\nLandau-Zener processes with self-interaction differs from those without\nself-interaction. Aside from gaining understandings of driven nonlinear\nLandau-Zener processes, our findings can be used to gauge the strength of\nnonlinearity and for efficient manipulation of the mean-field dynamics of\nmany-body systems.", "category": "cond-mat_other" }, { "text": "Collisional and molecular spectroscopy in an ultracold Bose-Bose mixture: The route toward a Bose-Einstein condensate of dipolar molecules requires the\nability to efficiently associate dimers of different chemical species and\ntransfer them to the stable rovibrational ground state. Here, we report on\nrecent spectroscopic measurements of two weakly bound molecular levels and\nnewly observed narrow d-wave Feshbach resonances. The data are used to improve\nthe collisional model for the Bose-Bose mixture 41K87Rb, among the most\npromising candidates to create a molecular dipolar BEC.", "category": "cond-mat_other" }, { "text": "Parametrically excited \"Scars\" in Bose-Einstein condensates: Parametric excitation of a Bose-Einstein condensate (BEC) can be realized by\nperiodically changing the interaction strength between the atoms. Above some\nthreshold strength, this excitation modulates the condensate density. We show\nthat when the condensate is trapped in a potential well of irregular shape,\ndensity waves can be strongly concentrated (\"scarred\") along the shortest\nperiodic orbits of a classical particle moving within the confining potential.\nWhile single-particle wave functions of systems whose classical counterpart is\nchaotic may exhibit rich scarring patterns, in BEC, we show that nonlinear\neffects select mainly those scars that are locally described by stripes.\nTypically, these are the scars associated with self retracing periodic orbits\nthat do not cross themselves in real space. Dephasing enhances this behavior by\nreducing the nonlocal effect of interference.", "category": "cond-mat_other" }, { "text": "Condensation of phonons in an ultracold Bose gas: We consider the generation of longitudinal phonons in an elongated\nBose-condensed gas at zero temperature due to parametric resonance as a result\nof the modulation of the transverse trap frequency. The nonlinear temporal\nevolution with account of the phonon-phonon interaction leads self-consistently\nto the formation of the stationary state with the macroscopic occupation of a\nsingle phonon quantum state.", "category": "cond-mat_other" }, { "text": "Diagnostics for the ground state phase of a spin-2 Bose-Einstein\n condensate: We propose a method to determine the singlet-pair energy of a spin-2\nBose-Einstein condensate (BEC). By preparing the initial populations in the\nmagnetic sublevels 0, 2, -2 with appropriate relative phases, we can obtain the\ncoefficient of the spin singlet-pair term from the spin exchange dynamics. This\nmethod is suitable for hyperfine states with short lifetimes, since only the\ninitial change in the population of each magnetic sublevel is needed. This\nmethod therefore enables the determination of the ground state phase of a\nspin-2 87Rb BEC at zero magnetic field, which is considered to lie in the\nimmediate vicinity of the boundary between the antiferromagnetic and cyclic\nphases. We also show that the initial state in which relative phases are\ncontrolled can be prepared by Raman processes.", "category": "cond-mat_other" }, { "text": "The strong form of the Levinson theorem for a distorted KP potential: We present a heuristic derivation of the strong form of the Levinson theorem\nfor one-dimensional quasi-periodic potentials. The particular potential chosen\nis a distorted Kronig-Penney model. This theorem relates the phase shifts of\nthe states at each band edge to the number of states crossing that edge, as the\nsystem evolves from a simple periodic potential to a distorted one. By applying\nthis relationship to the two edges of each energy band, the modified Levinson\ntheorem for quasi-periodic potentials is derived. These two theorems differ\nfrom the usual ones for isolated potentials in non-relativistic and\nrelativistic quantum mechanics by a crucial alternating sign factor $(-1)^{s}$,\nwhere $s$ refers to the adjacent gap or band index, as explained in the text.\nWe also relate the total number of bound states present in each energy gap due\nto the distortion to the phase shifts at its edges. At the end we present an\noverall relationship between all of the phase shifts at the band edges and the\ntotal number of bound states present.", "category": "cond-mat_other" }, { "text": "Comment on pressure driven flow of superfluid $^4$He through a nanopipe\n (Botimer and Taborek 2016): Botimer and Taborek (2016) measured the mass flux of superfluid $^4$He\nthrough a capillary into an evacuated chamber for various temperatures and\npressures of the reservoir chamber. They found a sharp transition from low flux\nat low pressures to high flux at large pressures. Here it is shown that the\nsuperfluid condition of chemical potential equality predicts the induced\ntemperature and also the transition pressure, which is attributed to the\ntransition from a semispherical cap to a pool of $^4$He at the exit of the\ncapillary. The results show that the two-fluid equations of superfluid flow,\nLandau's phonon-roton theory, and Feynman's critical vortex theory are\nunnecessary for a quantitative account of the measured transition pressure.", "category": "cond-mat_other" }, { "text": "CHEERS: A tool for Correlated Hole-Electron Evolution from Real-time\n Simulations: We put forward a practical nonequilibrium Green's function (NEGF) scheme to\nperform real-time evolutions of many-body interacting systems driven out of\nequilibrium by external fields. CHEERS is a computational tool to solve the\nNEGF equation of motion in the so called generalized Kadanoff-Baym ansatz and\nit can be used for model systems as well as first-principles Hamiltonians.\nDynamical correlation (or memory) effects are added to the Hartree-Fock\ndynamics through a many-body self-energy. Applications to time-dependent\nquantum transport, time-resolved photoabsorption and other ultrafast phenomena\nare discussed.", "category": "cond-mat_other" }, { "text": "Bose-Einstein condensation in an optical lattice: In this paper we develop an analytic expression for the critical temperature\nfor a gas of ideal bosons in a combined harmonic lattice potential, relevant to\ncurrent experiments using optical lattices. We give corrections to the critical\ntemperature arising from effective mass modifications of the low energy\nspectrum, finite size effects and excited band states. We compute the critical\ntemperature using numerical methods and compare to our analytic result. We\nstudy condensation in an optical lattice over a wide parameter regime and\ndemonstrate that the critical temperature can be increased or reduced relative\nto the purely harmonic case by adjusting the harmonic trap frequency. We show\nthat a simple numerical procedure based on a piecewise analytic density of\nstates provides an accurate prediction for the critical temperature.", "category": "cond-mat_other" }, { "text": "Dynamical equations for time-ordered Green's functions: from the Keldysh\n time-loop contour to equilibrium at finite and zero temperature: We study the dynamical equation of the time-ordered Green's function at\nfinite temperature. We show that the time-ordered Green's function obeys a\nconventional Dyson equation only at equilibrium and in the limit of\nzero-temperature. In all other cases, i.e. finite-temperature at equilibrium or\nnon-equilibrium, the time-ordered Green's function obeys instead a modified\nDyson equation. The derivation of this result is obtained from the general\nformalism of the non-equilibrium Green's functions on the Keldysh time-loop\ncontour. At equilibrium, our result is fully consistent with the Matsubara\ntemperature Green's function formalism and also justifies rigorously the\ncorrection terms introduced in an ad hoc way with Hedin and Lundqvist. Our\nresults show that one should use the appropriate dynamical equation for the\ntime-ordered Green's function when working beyond the equilibrium\nzero-temperature limit.", "category": "cond-mat_other" }, { "text": "Highly sensitive and broadband carbon nanotube radio-frequency\n single-electron transistor: We have investigated radio-frequency single-electron transistor (RF-SET)\noperation of single-walled carbon nanotube quantum dots in the strong tunneling\nregime. At 4.2 K and carrier frequency 754.2 MHz, we reach a charge sensitivity\nof 2.3e-6 e/Hz^(1/2) over a bandwidth of 85 MHz. Our results indicate a\ngain-bandwidth product of 3.7e13 Hz^(3/2)/e, which is by one order of magnitude\nbetter than for typical RF-SETs.", "category": "cond-mat_other" }, { "text": "Intrinsic leakage and adsorption currents associated with the\n electrocaloric effect in multilayer capacitors: During the last few years, the increasing demand of energy for refrigeration\napplications has relived the interest of the scientific community in the study\nof alternative methods to the traditional gas-based refrigeration. Within this\nframework, the use of solid state refrigeration based on the electrocaloric\neffect reveals itself as one of the most promising technologies. In this work,\nwe analyze how the temperature change associated with the electrocaloric effect\nshows a correlation with the electrical properties of a commercial multilayer\ncapacitor. In that sense we established a clear relation between the adsorption\ncurrents and the temperature change produced by the electrocaloric effect.\nAdditionally, intrinsic leakage currents are responsible for the sample heating\ndue to the Joule effect. These well distinguished contributions can be useful\nduring the design of solid state refrigeration devices based on the\nelectrocaloric effect.", "category": "cond-mat_other" }, { "text": "Quantum effects in the H-bond symmetrization and in the thermodynamic\n properties of high pressure ice: We investigate the structural and thermodynamic properties of high-pressure\nice by incorporating quantum anharmonicity at a non-perturbative level. Quantum\nfluctuations reduce the critical pressure of the phase transition between phase\nVIII (with asymmetric H-bonds) and phase X (with symmetric H-bonds) by 65 GPa\nfrom its classical value of 116 GPa at 0K. Moreover, quantum effects make it\ntemperature-independent over a wide temperature range (0K-300K), in agreement\nwith experimental estimates obtained through vibrational spectroscopy and in\nstriking contrast to the strong temperature dependence found in the classical\napproximation. The equation of state shows fingerprints of the transition in\naccordance with experimental evidence. Additionally, we demonstrate that,\nwithin our approach, proton disorder in phase VII has a negligible impact on\nthe occurrence of phase X. Finally, we reproduce with high accuracy the 10 GPa\nisotope shift due to the hydrogen-to-deuterium substitution.", "category": "cond-mat_other" }, { "text": "Simplified feedback control system for Scanning Tunneling Microscopy: A Scanning Tunneling Microscope (STM) is one of the most important scanning\nprobe tools available to study and manipulate matter at the nanoscale. In a\nSTM, a tip is scanned on top of a surface with a separation of a few \\AA.\nOften, the tunneling current between tip and sample is maintained constant by\nmodifying the distance between the tip apex and the surface through a feedback\nmechanism acting on a piezoelectric transducer. This produces very detailed\nimages of the electronic properties of the surface. The feedback mechanism is\nnearly always made using a digital processing circuit separate from the user\ncomputer. Here we discuss another approach, using a computer and data\nacquisition through the USB port. We find that it allows succesful ultra low\nnoise studies of surfaces at cryogenic temperatures. We show results on\ndifferent compounds, a type II Weyl semimetal (WTe$_2$), a quasi\ntwo-dimensional dichalcogenide superconductor (2H-NbSe$_2$), a magnetic Weyl\nsemimetal (Co$_3$Sn$_2$S$_2$) and an iron pnictide superconductor (FeSe).", "category": "cond-mat_other" }, { "text": "Observation of an Efimov-like resonance in ultracold atom-dimer\n scattering: The field of few-body physics has originally been motivated by understanding\nnuclear matter. New model systems to experimentally explore few-body quantum\nsystems can now be realized in ultracold gases with tunable interactions.\nAlbeit the vastly different energy regimes of ultracold and nuclear matter (peV\nas compared to MeV), few-body phenomena are universal for near-resonant\ntwo-body interactions. Efimov states represent a paradigm for universal\nthree-body states, and evidence for their existence has been obtained in\nmeasurements of three-body recombination in an ultracold gas of caesium atoms.\nInteracting samples of halo dimers can provide further information on universal\nfew-body phenomena. Here we study interactions in an optically trapped mixture\nof such halo dimers with atoms, realized in a caesium gas at nanokelvin\ntemperatures. We observe an atom-dimer scattering resonance, which we interpret\nas being due to a trimer state hitting the atom-dimer threshold. We discuss the\nclose relation of this observation to Efimov's scenario, and in particular to\natom-dimer Efimov resonances.", "category": "cond-mat_other" }, { "text": "Atoms in boxes: from confined atoms to electron-atom scattering: We show that both confined atoms and electron-atom scattering can be\ndescribed by a unified basis set method. The central idea behind this method is\nto place the atom inside a hard potential sphere, enforced by a standard Slater\ntype basis set multiplied by a cutoff factor. For confined atoms, where the\nwall is placed close to the atomic nucleus, we show how the energy of the\nhighest occupied atomic orbital and the static polarizability of helium and\nneon atoms evolve with the confinement radius. To our knowledge, these are the\nfirst confined atom polarizability calculations that include correlation,\nthrough the use of time-dependent density-functional theory. By placing the\natom in a large spherical box, with a wall outside the electron density, we\nobtain scattering phase shifts using a recently developed method [M. van\nFaassen, A. Wasserman, E. Engel, F. Zhang, and K. Burke, Phys. Rev. Lett. {\\bf\n99}, 043005 (2007)]. We show that the basis set method gives identical results\nto previously obtained phase shifts for $e$-H and $e$-He${}^{+}$ scattering.", "category": "cond-mat_other" }, { "text": "Localization by entanglement: We study the localization of bosonic atoms in an optical lattice, which\ninteract in a spatially confined region. The classical theory predicts that\nthere is no localization below a threshold value for the strength of\ninteraction that is inversely proportional to the number of participating\natoms. In a full quantum treatment, however, we find that localized states\nexist for arbitrarily weak attractive or repulsive interactions for any number\n($>1$) of atoms. We further show, using an explicit solution of the\ntwo-particle bound state and an appropriate measure of entanglement, that the\nentanglement tends to a finite value in the limit of weak interactions. Coupled\nwith the non-existence of localization in an optimized quantum product state,\nwe conclude that the localization exists by virtue of entanglement.", "category": "cond-mat_other" }, { "text": "Three-Body Recombination of Identical Bosons with a Large Positive\n Scattering Length at Nonzero Temperature: For identical bosons with a large scattering length, the dependence of the\n3-body recombination rate on the collision energy is determined in the\nzero-range limit by universal functions of a single scaling variable. There are\nsix scaling functions for angular momentum zero and one scaling function for\neach higher partial wave. We calculate these universal functions by solving the\nSkorniakov--Ter-Martirosian equation. The results for the 3-body recombination\nas a function of the collision energy are in good agreement with previous\nresults from solving the 3-body Schroedinger equation for 4He atoms. The\nuniversal scaling functions can be used to calculate the 3-body recombination\nrate at nonzero temperature. We obtain an excellent fit to the data from the\nInnsbruck group for 133Cs atoms with a large positive scattering length.", "category": "cond-mat_other" }, { "text": "Correlation energy of two electrons in a ball: We study the ground-state correlation energy $E_{\\rm c}$ of two electrons of\nopposite spin confined within a $D$-dimensional ball ($D \\ge 2$) of radius $R$.\nIn the high-density regime, we report accurate results for the exact and\nrestricted Hartree-Fock energy, using a Hylleraas-type expansion for the former\nand a simple polynomial basis set for the latter. By investigating the exact\nlimiting correlation energy $E_{\\rm c}^{(0)} = \\lim_{R \\to 0} \\Ec$ for various\nvalues of $D$, we test our recent conjecture [J. Chem. Phys. {\\bf 131} (2009)\n241101] that, in the large-$D$ limit, $E_{\\rm c}^{(0)} \\sim -\\delta^2/8$ for\nany spherically-symmetric confining external potential, where $\\delta=1/(D-1)$.", "category": "cond-mat_other" }, { "text": "The influence of the optical Stark effect on chiral tunneling in\n graphene: The influences of intense coherent laser fields on the transport properties\nof a single layer graphene are investigated by using the finite-difference\ntime-domain method. Under an intense laser field, the valence band and\nconduction band states mix via the optical Stark effect. The chiral symmetry of\nDirac electrons is broken and the perfect chiral tunneling is strongly\nsuppressed.", "category": "cond-mat_other" }, { "text": "Formation of vortices in a dense Bose-Einstein condensate: A relaxation method is employed to study a rotating dense Bose-Einstein\ncondensate beyond Thomas-Fermi approximation. We use a slave-boson model to\ndescribe the strongly interacting condensate and derive a generalized\nnon-linear Schr\\\"odinger equation with kinetic term for the rotating\ncondensate. In comparison with previous calculations, based on Thomas-Fermi\napproximation, significant improvements are found in regions, where the\ncondensate in a trap potential is not smooth. The critical angular velocity of\nthe vortex formation is higher than in the Thomas-Fermi prediction.", "category": "cond-mat_other" }, { "text": "Electrically probing photonic bandgap phenomena in contacted defect\n nanocavities: We demonstrate an electrically tunable two dimensional photonic crystal\nnanocavity containing InAs self assembled quantum dots. Photoluminescence and\nelectroluminescence measurements are combined to probe the cavity mode\nstructure and demonstrate a local electrical contact to the quantum dots.\nMeasurements performed as a function of the electric field enable us to probe\nthe capture, relaxation and recombination dynamics of photogenerated carriers\ninside the quantum dots emitting into a modified photonic environment.\nFurthermore, the two dimensional photonic crystal is probed by spatially\ndependent photocurrent spectroscopy indicating a 3.5x enhancement of the local\nradiative lifetime of the QDs inside the photonic crystal environment.", "category": "cond-mat_other" }, { "text": "Graphite vs graphene: scientific background: Nobel Prize in Physics 2010 was given for \"groundbreaking experiments\nregarding the two-dimensional material graphene.\" In fact, before graphene has\nbeen extracted from graphite and measured, some of its fundamental physical\nproperties have already been experimentally uncovered in bulk graphite. In this\nLetter to the Nobel Committee we propose to include those findings in the\nScientific Background", "category": "cond-mat_other" }, { "text": "Collisional de-excitation in a quasi-2D degenerate Bose gas: We separate a Bose-Einstein condensate into an array of 2D sheets using a 1D\noptical lattice, and then excite quantized vibrational motion in the direction\nnormal to the sheets. Collisions between atoms induce vibrational\nde-excitation, transferring the large excitation energy into back-to-back\noutgoing atoms, imaged as rings in the 2D plane. The ring diameters correspond\nto vibrational energy level differences, and edge-on imaging allows\nidentification of the final vibrational states. Time dependence of these data\nprovides a nearly complete characterization of the decay process including the\nenergies, populations, and lifetimes of the lowest two excited vibrational\nlevels. The measured decay rates represent a suppression of collisional\nde-excitation due to the reduced dimensionality, a matter wave analog to\ninhibited spontaneous emission.", "category": "cond-mat_other" }, { "text": "The Fast Wandering of Slow Birds: I study a single \"slow\" bird moving with a flock of birds of a different, and\nfaster (or slower) species. I find that every \"species\" of flocker has a\ncharacteristic speed $\\gamma\\ne v_0$, where $v_0$ is the mean speed of the\nflock, such that, if the speed $v_s$ of the \"slow\" bird equals $\\gamma$, it\nwill randomly wander transverse to the mean direction of flock motion far\nfaster than the other birds will: its mean-squared transverse displacement will\ngrow in $d=2$ with time $t$ like $t^{5/3}$, in contrast to $t^{4/3}$ for the\nother birds. In $d=3$, the slow bird's mean squared transverse displacement\ngrows like $t^{5/4}$, in contrast to $t$ for the other birds. If $v_s\\neq\n\\gamma$, the mean-squared displacement of the \"slow\" bird crosses over from\n$t^{5/2}$ to $t^{4/3}$ scaling in $d=2$, and from $t^{5/4}$ to $t$ scaling in\n$d=3$, at a time $t_c$ that scales according to $t_c \\propto|v_s-\\gamma|^{-2}$.", "category": "cond-mat_other" }, { "text": "Fermi Condensates: Ultracold atomic gases have proven to be remarkable model systems for\nexploring quantum mechanical phenomena. Experimental work on gases of fermionic\natoms in particular has seen large recent progress including the attainment of\nso-called Fermi condensates. In this article we will discuss this recent\ndevelopment and the unique control over interparticle interactions that made it\npossible.", "category": "cond-mat_other" }, { "text": "Matter Wave Interference Pattern in the collision of bright solitons\n (Bose Einstein condensates) in a time dependent trap: We show that it is possible to observe matter wave interference patterns in\nthe collision of bright solitons (Bose Einstein condensates) without free\nballistic expansion for suitable choices of scattering length and time\ndependent trap.", "category": "cond-mat_other" }, { "text": "Hyperspherical Description of the Degenerate Fermi Gas: S-wave\n Interactions: We present a unique theoretical description of the physics of the spherically\ntrapped $N$-atom degenerate Fermi gas (DFG) at zero temperature based on an\nordinary Schr\\\"{o}dinger equation with a microscopic, two body interaction\npotential. With a careful choice of coordinates and a variational wavefunction,\nthe many body Schr\\\"{o}dinger equation can be accurately described by a\n\\emph{linear}, one dimensional effective Schr\\\"{o}dinger equation in a single\ncollective coordinate, the rms radius of the gas. Comparisons of the energy,\nrms radius and peak density of ground state energy are made to those predicted\nby Hartree-Fock (HF). Also the lowest radial excitation frequency (the\nbreathing mode frequency) agrees with a sum rule calculation, but deviates from\na HF prediction.", "category": "cond-mat_other" }, { "text": "Boson Representation of Spin Operators: The derivation of the boson representation of spin operators is given which\nreproduces the Holstein-Primakoff and Dyson-Maleev transformations in the\ncorresponding cases. The suggested formalism allows to address some subtle\nissues which appear crucial for treating certain class of problems. Moreover,\nthe transformation is suggested which is naturally related to the symmetry of\nthe spin systems.", "category": "cond-mat_other" }, { "text": "On the absorption spectrum of noble gases at the arc spectrum limit: Rydberg spectral lines of an atom are sometimes superimposed on the\ncontinuous spectrum of a different configuration. Effects of interaction among\ndifferent configurations in one of these cases are theoretically investigated,\nand a formula is obtained that describes the behavior of absorption spectrum\nintensity. This offers qualitative justification of some experimental results\nobtained by BEUTLER in studies of absorption arc spectra of noble gases and\n$I^b$ spectra of some metal vapors.", "category": "cond-mat_other" }, { "text": "Theory of correlations between ultra-cold bosons released from an\n optical lattice: In this paper we develop a theoretical description of the correlations\nbetween ultra-cold bosons after free expansion from confinement in an optical\nlattice. We consider the system evolution during expansion and give criteria\nfor a far field regime. We develop expressions for first and second order\ntwo-point correlations based on a variety of commonly used approximations to\nthe many-body state of the system including Bogoliubov, meanfield decoupling,\nand particle-hole perturbative solution about the perfect Mott-insulator state.\nUsing these approaches we examine the effects of quantum depletion and pairing\non the system correlations. Comparison with the directly calculated correlation\nfunctions is used to justify a Gaussian form of our theory from which we\ndevelop a general three-dimensional formalism for inhomogeneous lattice systems\nsuitable for numerical calculations of realistic experimental regimes.", "category": "cond-mat_other" }, { "text": "Nonlinear Quantum Electrodynamics in Dirac materials: Classical electromagnetism is linear. However, fields can polarize the vacuum\nDirac sea, causing quantum nonlinear electromagnetic phenomena, e.g.,\nscattering and splitting of photons, that occur only in very strong fields\nfound in neutron stars or heavy ion colliders.We show that strong nonlinearity\narises in Dirac materials at much lower fields $\\sim 1\\:\\text{T}$, allowing us\nto explore the nonperturbative, extremely high field limit of quantum\nelectrodynamics in solids. We explain recent experiments in a unified framework\nand predict a new class of nonlinear magneto-electric effects, including a\nmagnetic enhancement of dielectric constant of insulators and a strong electric\nmodulation of magnetization. We propose experiments and discuss the\napplications in novel materials.", "category": "cond-mat_other" }, { "text": "Classical and quantum dynamics of pulsating instability in a\n Bose-Einstein condensate in an optical lattice: We study the dynamics of a Bose-Einstein condensate (BEC) in a one\ndimensional optical lattice in the limit of weak atom-atom interactions.\nNumerically we find that a BEC may develop a pulsating instability in which\natoms nearly periodically collect themselves into a pulse and subsequently\ndisperse back into the initial homogeneous state. A qualitative explanation of\nthe quasi-periodic behavior is given by drawing an analogy with a double-well\nsystem. In an extension we introduce quantum effects approximately within\nTruncated Wigner Approximation (TWA). In pure classical mean field theory the\ncondensate shows an undamped pulsating instability, whereas we have observed a\ndamping in the oscillation when we average over many stochastic realizations.", "category": "cond-mat_other" }, { "text": "The Structure of Integrable One-Dimensional Systems: We explain the relationship between the classical description of an\nintegrable system in terms of invariant tori and action-angle variables, and\nthe quantum description in terms of the asymptotic Bethe ansatz.", "category": "cond-mat_other" }, { "text": "Electronic Control and Readout of Qubit States in Solid State Quantum\n Computing Systems: We demonstrate that an $n^+/i/n^+$ junction is the most suitable candidate\nfor electronic control and readout of qubit states in quantum computing systems\nbased on shallow impurities. The signature of this system is that the\n$n^+-$regions serve as metallic electrodes separated form the $i-$region by a\nself-induced barrier (internal workfunction). The $n^+/i/n^+$ system mimics the\nproperties of a metal-vacuum-metal junction with the qubit (impurity atom)\nplaced in a ``vacuum'' $i$-region between two ``metallic'' $n^+$ electrodes. We\nwill show that the self-induced barrier exists in a sufficiently wide range of\nthe concentration of dopants in the $n^+$-semiconductor (e.g. up to $10^{21}$\ncm$^{-3}$ for Si) and its height can be controlled by tuning the doping level.\nA shallow donor placed in a vacuum $i$-region will be populated with one\nelectron in equilibrium. In the case of Li donor in Si the $n^+$-electrodes\nwill be used for a precision placement of the Li atom during the growth\nprocess; for voltage control and manipulation of the qubit states; and for a\nqubit readout by means of the optically stimulated resonant tunnelling. Another\nimportant feature of our system is that the qubit states (first two lowest\nenergy levels of Li in Si) are separated by an energy gap from a continuum of\nthe many-body states of the controlling electrodes.", "category": "cond-mat_other" }, { "text": "Numerical study of magnetic field induced ordering in BaCuSi$_2$O$_6$\n and related systems: Thermodynamics of spin dimer system BaCuSi_2O_6 is studied using a quantum\nMonte Carlo calculation (QMC) and a bond-operator mean field theory. We propose\nthat a new type of boson, which, rather than being hard-core, allows up to two\noccupancy at each site, is responsible for the Bose Einstein condensation of\nfield induced ordering. Its superfluid density is identified as the square of\nthe in-plane staggered magnetization m_{xy} in the ordered phase. We also\ncompare our QMC result of the spin Heisenberg model to those predicted by mean\nfield theory as well as by the simple hard core boson model for both large and\nsmall intra-dimer coupling J. The asymmetry of the phase diagram of m_{xy}(h)\nof small coupling J in related systems such as NiCl_2-4SC(NH_2)_2 is explained\nwith our new boson operator.", "category": "cond-mat_other" }, { "text": "Magnetism and structure of magnetic multilayers based on the fully spin\n polarized Heusler alloys Co2MnGe and Co2MnSn: Our Introduction starts with a short general review of the magnetic and\nstructural properties of the Heusler compounds which are under discussion in\nthis book. Then, more specifically, we come to the discussion of our\nexperimental results on multilayers composed of the Heusler alloys Co2MnGe and\nCo2MnSn with V or Au as interlayers. The experimental methods we apply combine\nmagnetization and magneto-resistivity measurements, x-ray diffraction and\nreflectivity, soft x-ray magnetic circular dichroism and spin polarized neutron\nreflectivity. We find that below a critical thickness of the Heusler layers at\ntypically dcr = 1.5 nm the ferromagnetic order is lost and spin glass order\noccurs instead. For very thin ferromagnetic Heusler layers there are\npeculiarities in the magnetic order which are unusual when compared to\nconventional ferromagnetic transition metal multilayer systems. In [Co2MnGe/Au]\nmultilayers there is an exchange bias shift at the ferromagnetic hysteresis\nloops at low temperatures caused by spin glass ordering at the interface. In\n[Co2MnGe/V] multilayers we observe an antiferromagnetic interlayer long range\nordering below a well defined Neel temperature originating from the dipolar\nstray fields at the magnetically rough Heusler layer interfaces.", "category": "cond-mat_other" }, { "text": "Coexisting Non-Equilibrium Condensates with Long-Range Spatial Coherence\n in Semiconductor Microcavities: Real and momentum space spectrally resolved images of microcavity polariton\nemission in the regime of condensation are investigated under non resonant\nexcitation using a laser source with reduced intensity fluctuations on the\ntimescale of the exciton lifetime. We observe that the polariton emission\nconsists of many macroscopically occupied modes. Lower energy modes are\nstrongly localized by the photonic potential disorder on a scale of few\nmicrons. Higher energy modes have finite k-vectors and are delocalized over\n10-15 microns. All the modes exhibit long range spatial coherence comparable to\ntheir size. We provide a theoretical model describing the behavior of the\nsystem with the results of the simulations in good agreement with the\nexperimental observations. We show that the multimode emission of the polariton\ncondensate is a result of its nonequilibrium character, the interaction with\nthe local photonic potential and the reduced intensity fluctuations of the\nexcitation laser.", "category": "cond-mat_other" }, { "text": "Annealing Effect for Supersolid Fraction in $^4$He: We report on experimental confirmation of the non-classical rotational\ninertia (NCRI) in solid helium samples originally reported by Kim and Chan. The\nonset of NCRI was observed at temperatures below ~400 mK. The ac velocity for\ninitiation of the NCRI suppression is estimated to be ~10 $\\mu$m/sec. After an\nadditional annealing of the sample at $T= 1.8$ K for 12 hours, ~ 10% relative\nincrease of NCRI fraction was observed. Then after repeated annealing with the\nsame conditions, the NCRI fraction was saturated. It differs from Reppy's\nobservation on a low pressure solid sample.", "category": "cond-mat_other" }, { "text": "Pairing fluctuations and the superfluid density through the BCS-BEC\n crossover: We derive an expression for the superfluid density of a uniform two-component\nFermi gas through the BCS-BEC crossover in terms of the thermodynamic potential\nin the presence of an imposed superfluid flow. Treating the pairing\nfluctuations in a Gaussian approximation following the approach of Nozi\\`eres\nand Schmitt-Rink, we use this definition of $\\rho_s$ to obtain an explicit\nresult which is valid at finite temperatures and over the full BCS-BEC\ncrossover. It is crucial that the BCS gap $\\Delta$, the chemical potential\n$\\mu$, and $\\rho_s$ all include the effect of fluctuations at the same level in\na self-consistent manner. We show that the normal fluid density $\\rho_n \\equiv\nn - \\rho_s$ naturally separates into a sum of contributions from Fermi BCS\nquasiparticles ($\\rho^F_{n}$) and Bose collective modes ($\\rho^B_{n}$). The\nexpression for $\\rho^F_{n}$ is just Landau's formula for a BCS Fermi superfluid\nbut now calculated over the BCS-BEC crossover. The expression for the Bose\ncontribution $\\rho^B_{n}$ is more complicated and only reduces to Landau's\nformula for a Bose superfluid in the extreme BEC limit, where all the fermions\nhave formed stable Bose pairs and the Bogoliubov excitations of the associated\nmolecular Bose condensate are undamped. In a companion paper, we present\nnumerical calculations of $\\rho_s$ using an expression equivalent to the one\nderived in this paper, over the BCS-BEC crossover, including unitarity, and at\nfinite temperatures.", "category": "cond-mat_other" }, { "text": "Coherent tunneling by adiabatic passage in an optical waveguide system: We report on the first experimental demonstration of light transfer in an\nengineered triple-well optical waveguide structure which provides a classic\nanalogue of Coherent Tunnelling by Adiabatic Passage (CTAP) recently proposed\nfor coherent transport in space of neutral atoms or electrons among\ntunneling-coupled optical traps or quantum wells [A.D. Greentree et al., Phys.\nRev. B 70, 235317 (2004); K. Eckert et al., Phys. Rev. A 70, 023606 (2004)].\nThe direct visualization of CTAP wavepacket dynamics enabled by our simple\noptical system clearly shows that in the counterintuitive passage scheme light\nwaves tunnel between the two outer wells without appreciable excitation of the\nmiddle well.", "category": "cond-mat_other" }, { "text": "Introduction to Spin-Polarized Ballistic Hot Electron Injection and\n Detection in Silicon: Ballistic hot electron transport overcomes the well-known problems of\nconductivity and spin lifetime mismatch that plagues spin injection in\nsemiconductors with ferromagnetic ohmic contacts. Through the spin-dependent\nmean-free-path, it also provides a means for spin detection after transport.\nExperimental results using these techniques (consisting of spin precession and\nspin-valve measurements) with Silicon-based devices reveals the exceptionally\nlong spin lifetime and high spin coherence induced by drift-dominated transport\nin the semiconductor. An appropriate quantitative model that accurately\nsimulates the device characteristics for both undoped and doped spin transport\nchannels is described; it can be used to determine the spin current velocity,\ndiffusion constant, and spin lifetime, constituting a spin \"Haynes-Shockley\"\nexperiment without time-of-flight techniques. A perspective on the future of\nthese methods is offered as summary.", "category": "cond-mat_other" }, { "text": "Semiclassical atom theory applied to solid-state physics: Using the semiclassical neutral atom theory, we extend to fourth order the\nmodified gradient expansion of the exchange energy of density functional\ntheory. This expansion can be applied both to large atoms and solid-state\nproblems. Moreover, we show that it can be employed to construct a simple and\nnon-empirical generalized gradient approximation (GGA) exchange-correlation\nfunctional competitive with state-of-the-art GGAs for solids, but also\nreasonably accurate for large atoms and ordinary chemistry.", "category": "cond-mat_other" }, { "text": "Quantum computing without qubit-qubit interactions: Quantum computing tries to exploit entanglement and interference to process\ninformation more efficiently than the best known classical solutions.\nExperiments demonstrating the feasibility of this approach have already been\nperformed. However, finding a really scalable and robust quantum computing\narchitecture remains a challenge for both, experimentalists and theoreticians.\nIn most setups decoherence becomes non-negligible when one tries to perform\nentangling gate operations using the coherent control of qubit-qubit\ninteractions. However, in this proceedings we show that two-qubit gate\noperations can be implemented even without qubit-qubit interactions and review\na recent quantum computing scheme by Lim et al. [Phys. Rev. Lett. 95, 030505\n(2005)] using only single photon sources (e.g. atom-cavity systems, NV colour\ncentres or quantum dots) and photon pair measurements.", "category": "cond-mat_other" }, { "text": "Mechanism of Electric Field Induced Conductance Transition in Molecular\n Organic Semiconductor Based Thin Films: We have studied the electrical field induced conductance transition in thin\nfilm of Perylenetetracarboxylic dianhydride sandwiched between two metal\nelectrodes, from an insulating state to conducting state with a high ON-OFF\nratio in those devices, where one of electrodes is either Al or Cu. Temperature\ndependence of resistivity shows semiconducting behavior in OFF-state, but it\nshows metallic behavior in the ON-state. Devices with a thin intermediate layer\nof LiF between metal electrode and organic layer, or devices fabricated in\nplanar configuration do not show switching behavior. All these suggest that\nconducting pathways are responsible for the electric field induced conductance\ntransition.", "category": "cond-mat_other" }, { "text": "The system of mobile ions in lattice models: Screening effects,\n thermodynamic and electrophysical properties: The lattice fluid model of the system with short range and long range Coulomb\ninteractions is suggested. In the framework of the collective variables method,\nthe screening of the Coulomb interactions in the bulk is considered. It is\nshown that the Debye length includes additional concentration dependence\ninversely proportional to the square root of the mean concentration of vacant\nsites like what is known at the plane boundary. The Coulomb interaction\ncontribution to the free energy of the system is calculated in the approach\nclose to the mean spherical approximation and is given in an analytical form.\nThe influence of the variation of the crystal field near the system boundary on\nthe structure and characteristics of the electric double layer is investigated.\nAs compared to the system with equal crystal potentials at the lattice sites\nthroughout the system the pronounced difference for the electric capacitance\nappears at low absolute values of the surface potential and it is more\npronounced for negative electric potentials. The capacitance diverges as the\npotential values at which the electric field tends to zero and attains negative\nvalues in regions of the surface potentials depending on their polarity and\nvalues of the surface crystal potential. Negative values of the capacitance may\nindicate the thermodynamic instability of the system that can result from\nneglecting the short range interaction contribution.", "category": "cond-mat_other" }, { "text": "Lattice solitons in quasicondensates: We analyze finite temperature effects in the generation of bright solitons in\ncondensates in optical lattices. We show that even in the presence of strong\nphase fluctuations solitonic structures with well defined phase profile can be\ncreated. We propose a novel family of variational functions which describe well\nthe properties of these solitons and account for the non-linear effects in the\nband structure. We discuss also the mobility and collisions of these localized\nwave packets.", "category": "cond-mat_other" }, { "text": "Comment on \"Exact results for survival probability in the multistate\n Landau-Zener model\": We correct the proof of Brundobler-Elser formula (BEF) provided in [2004\n\\textit{J. Phys. B: At. Mol. Opt. Phys.} \\textbf{37} 4069] and continued in\nAppendix of [2005 \\textit{J. Phys. B: At. Mol. Opt. Phys.} \\textbf{38} 907].\nAfter showing that some changes of variables employed in these articles are\nused erroneously, we propose an alternative change of variables which solves\nthe problem. In our proof, we reveal the connection between the BEF for a\ngeneral $N$-level Landau-Zener system and the exactly solvable bow-tie model.\nThe special importance of the diabatic levels with maximum/minimum slope is\nemphasized throughout.", "category": "cond-mat_other" }, { "text": "Onset of thermally driven self-motion of a current filament in a\n bistable semiconductor structure: We perform an analytical investigation of the bifurcation from static to\ntraveling current density filaments in a bistable semiconductor structure with\nS-shaped current-voltage characteristic. Joule self-heating of a semiconductor\nstructure and the effect of temperature on electron transport are consistently\ntaken into account in the framework of a generic reaction-diffusion model with\nglobal coupling. It is shown that the self-heating is capable to induce\ntranslation instability which leads to spontaneous onset of lateral self-motion\nof the filament along the structure. This may occur in a wide class of\nsemiconductor structures whose bistability is caused by impact ionization due\nto the negative effect of temperature on the impact ionization rate. The\nincrement of the translation mode and the instability threshold are determined\nanalytically.", "category": "cond-mat_other" }, { "text": "On non-markovian nature of stock trading: Using a relationship between the moments of the probability distribution of\ntimes between the two consecutive trades (intertrade time distribution) and the\nmoments of the distribution of a daily number of trades we show, that the\nunderlying point process generating times of the trades is an essentially\nnon-markovian long-range memory one. Further evidence for the long-range memory\nnature of this point process is provided by the powerlike correlation between\nthe intertrade time intervals. The data set includes all trades in EESR stock\non the Moscow International Currency Exchange in January 2003 - September 2003\nand in Siemens, Commerzbank and Karstadt stocks traded on the Xetra electronic\nstock exchange of Deutsche Boerse in October 2002.", "category": "cond-mat_other" }, { "text": "On reality of dynamical matrix: The symmetry properties of the dynamical matrix are well described in\nmultiple classic textbooks. This short paper revisits the issue to demonstrate\nalternative form of dynamical matrix which explicitly shows its symmetry and\nreality in common cases.", "category": "cond-mat_other" }, { "text": "Wave equation of the scalar field and superfluids: The new formal analogy between superfluid systems and cosmology, which\nemerges by taking into account the back-reaction of the vacuum to the quanta of\nsound waves \\cite{noi}, enables us to put forward some common features between\nthese two different areas of physics. We find the condition that allows us to\njustify a General Relativity (GR) derivation of the hydrodynamical equation for\nthe superfluid in a four-dimensional space whose metric is the Unruh one\n\\cite{Unruh}. Furthermore we show how, in the particular case taken into\naccount, our hydrodynamical equation can be deduced within a four-dimensional\nspace from the wave equation of a massless scalar field.", "category": "cond-mat_other" }, { "text": "Matter sound waves in two-component Bose-Einstein condensates: The creation and propagation of sound waves in two-component Bose-Einstein\ncondensates (BEC) are investigated and a new method of wave generation in\nbinary BEC mixtures is proposed. The method is based on a fast change of the\ninter-species interaction constant and is illustrated for two experimental\nsettings: a drop-like condensate immersed into a second large repulsive\ncondensate, and a binary mixture of two homogeneous repulsive BEC's. A\nmathematical model based on the linearized coupled Gross-Pitaevskii equations\nis developed and explicit formulae for the space and time dependence of sound\nwaves are provided. Comparison of the analytical and numerical results shows\nexcellent agreement, confirming the validity of the proposed approach.", "category": "cond-mat_other" }, { "text": "Spin-polarized transport in ferromagnetic multilayered semiconductor\n nanostructures: The occurrence of inhomogeneous spin-density distribution in multilayered\nferromagnetic diluted magnetic semiconductor nanostructures leads to strong\ndependence of the spin-polarized transport properties on these systems. The\nspin-dependent mobility, conductivity and resistivity in\n(Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a\nfunction of temperature, scaled by the average magnetization of the diluted\nmagnetic semiconductor layers. An increase of the resistivity near the\ntransition temperature is obtained. We observed that the spin-polarized\ntransport properties changes strongly among the three materials.", "category": "cond-mat_other" }, { "text": "Quantum dynamics in view of Einstein's theory of Brownian motion: A quantum-mechanical version of Einstein's 1905 theory of Brownian motion is\npresented. Starting from the Hamiltonian dynamics of an isolated composite of\nobjective and environmental systems, subdynamics for the objective system is\nderived in the spirit of Einstein. The resulting master equation is found to\nhave the Lindblad structure.", "category": "cond-mat_other" }, { "text": "Transport in ultradilute solutions of $^3$He in superfluid $^4$He: We calculate the effect of a heat current on transporting $^3$He dissolved in\nsuperfluid $^4$He at ultralow concentration, as will be utilized in a proposed\nexperimental search for the electric dipole moment of the neutron (nEDM). In\nthis experiment, a phonon wind will generated to drive (partly depolarized)\n$^3$He down a long pipe. In the regime of $^3$He concentrations $\\tilde <\n10^{-9}$ and temperatures $\\sim 0.5$ K, the phonons comprising the heat current\nare kept in a flowing local equilibrium by small angle phonon-phonon\nscattering, while they transfer momentum to the walls via the $^4$He first\nviscosity. On the other hand, the phonon wind drives the $^3$He out of local\nequilibrium via phonon-$^3$He scattering. For temperatures below $0.5$ K, both\nthe phonon and $^3$He mean free paths can reach the centimeter scale, and we\ncalculate the effects on the transport coefficients. We derive the relevant\ntransport coefficients, the phonon thermal conductivity and the $^3$He\ndiffusion constants from the Boltzmann equation. We calculate the effect of\nscattering from the walls of the pipe and show that it may be characterized by\nthe average distance from points inside the pipe to the walls. The temporal\nevolution of the spatial distribution of the $^3$He atoms is determined by the\ntime dependent $^3$He diffusion equation, which describes the competition\nbetween advection by the phonon wind and $^3$He diffusion. As a consequence of\nthe thermal diffusivity being small compared with the $^3$He diffusivity, the\nscale height of the final $^3$He distribution is much smaller than that of the\ntemperature gradient. We present exact solutions of the time dependent\ntemperature and $^3$He distributions in terms of a complete set of normal\nmodes.", "category": "cond-mat_other" }, { "text": "Comparison of strong coupling regimes in bulk GaAs, GaN and ZnO\n semiconductor microcavities: Wide bandgap semiconductors are attractive candidates for polariton-based\ndevices operating at room temperature. We present numerical simulations of\nreflectivity, transmission and absorption spectra of bulk GaAs, GaN and ZnO\nmicrocavities, in order to compare the particularities of the strong coupling\nregime in each system. Indeed the intrinsic properties of the excitons in these\nmaterials result in a different hierarchy of energies between the valence-band\nsplitting, the effective Rydberg and the Rabi energy, defining the\ncharacteristics of the exciton-polariton states independently of the quality\nfactor of the cavity. The knowledge of the composition of the polariton\neigenstates is central to optimize such systems. We demonstrate that, in ZnO\nbulk microcavities, only the lower polaritons are good eigenstates and all\nother resonances are damped, whereas upper polaritons can be properly defined\nin GaAs and GaN microcavities.", "category": "cond-mat_other" }, { "text": "Absorbing photonic crystals for thin film photovoltaics: The absorption of thin hydrogenated amorphous silicon layers can be\nefficiently enhanced through a controlled periodic patterning. Light is trapped\nthrough coupling with photonic Bloch modes of the periodic structures, which\nact as an absorbing planar photonic crystal. We theoretically demonstrate this\nabsorption enhancement through one or two dimensional patterning, and show the\nexperimental feasibility through large area holographic patterning. Numerical\nsimulations show over 50% absorption enhancement over the part of the solar\nspectrum comprised between 380 and 750nm. It is experimentally confirmed by\noptical measurements performed on planar photonic crystals fabricated by laser\nholography and reactive ion etching.", "category": "cond-mat_other" }, { "text": "Bose Einstein Condensation of incommensurate solid 4He: It is pointed out that simulation computation of energy performed so far\ncannot be used to decide if the ground state of solid 4He has the number of\nlattice sites equal to the number of atoms (commensurate state) or if it is\ndifferent (incommensurate state). The best variational wave function, a shadow\nwave function, gives an incommensurate state but the equilibrium concentration\nof vacancies remains to be determined. In order to investigate the presence of\na supersolid phase we have computed the one--body density matrix in solid 4He\nfor the incommensurate state by means of the exact Shadow Path Integral Ground\nState projector method. We find a vacancy induced Bose Einstein condensation of\nabout 0.23 atoms per vacancy at a pressure of 54 bar. This means that bulk\nsolid 4He is supersolid at low enough temperature if the exact ground state is\nincommensurate.", "category": "cond-mat_other" }, { "text": "Improved modeling of Coulomb effects in nanoscale Schottky-barrier FETs: We employ a novel multi-configurational self-consistent Green's function\napproach (MCSCG) for the simulation of nanoscale Schottky-barrier field-effect\ntransistors. This approach allows to calculate the electronic transport with a\nseamless transition from the single-electron regime to room temperature\nfield-effect transistor operation. The particular improvement of the MCSCG\nstems from a division of the channel system into a small subsystem of\nresonantly trapped states for which a many-body Fock space becomes feasible and\na strongly coupled rest which can be treated adequately on a conventional\nmean-field level. The Fock space description allows for the calculation of\nfew-electron Coulomb charging effects beyond mean-field.\n We compare a conventional Hartree non-equilibrium Green's function\ncalculation with the results of the MCSCG approach. Using the MCSCG method\nCoulomb blockade effects are demonstrated at low temperatures while under\nstrong nonequilibrium and room temperature conditions the Hartree approximation\nis retained.", "category": "cond-mat_other" }, { "text": "Ohmic and non-Ohmic Andreev transport through an interface between\n superconductor and hopping insulator: Dramatic role of barrier properties: At low temperatures and voltages tunneling transport through an interface\nbetween a superconductor and hopping insulator is dominated by coherent\ntwo-electron tunneling between the Cooper-pair condensate and pairs of\nlocalized states, see Kozub et al., PRL 96, 107004 (2006). By detailed analysis\nof such transport we show that the interface resistance is extremely sensitive\nto the properties of the tunneling barriers, as well as to asymptotic behavior\nof the localized states. In particular, dramatic cancellation takes place for\nhydrogen-like impurities and ideal barrier. However, some disorder can lift the\ncancellations restoring the interface transport. We also study non-Ohmic\nbehavior of the interface resistor and show that it is sensitive to the Coulomb\ncorrelation of the occupation probabilities of the involved localized states.\nIt is expected that non-Ohmic contribution to I-V-curve will experience\npronounced mesoscopic (fingerprint) fluctuations.", "category": "cond-mat_other" }, { "text": "Chiral Symmetry and Electron Spin Relaxation of Lithium Donors in\n Silicon: We report theoretical and experimental studies of the longitudinal electron\nspin and orbital relaxation time of interstitial Li donors in $^{28}$Si. We\npredict that despite the near-degeneracy of the ground-state manifold the spin\nrelaxation times are extremely long for the temperatures below 0.3 K. This\nprediction is based on a new finding of the chiral symmetry of the donor\nstates, which presists in the presence of random strains and magnetic fields\nparallel to one of the cubic axes. Experimentally observed kinetics of\nmagnetization reversal at 2.1 K and 4.5 K are in a very close agreement with\nthe theory. To explain these kinetics we introduced a new mechanism of spin\ndecoherence based on a combination of a small off-site displacement of the Li\natom and an umklapp phonon process. Both these factors weakly break chiral\nsymmetry and enable the long-term spin relaxation.", "category": "cond-mat_other" }, { "text": "Magnetic Phase Transition in FeRh: Density functional calculations are performed to investigate the phase\ntransition in FeRh alloy. The effective exchange coupling, the critical\ntemperature of magnetic phase transition and the adiabatic spin wave spectrum\nhave been obtained. Different contributions to the free energy of different\nphases are estimated. It has been found that the antiferro-ferromagnetic\ntransition in FeRh occurs mostly due to the spin wave excitations.", "category": "cond-mat_other" }, { "text": "Self-Adaptive Spike-Time-Dependent Plasticity of Metal-Oxide Memristors: Metal-oxide memristors have emerged as promising candidates for hardware\nimplementation of artificial synapses - the key components of high-performance,\nanalog neuromorphic networks - due to their excellent scaling prospects. Since\nsome advanced cognitive tasks require spiking neuromorphic networks, which\nexplicitly model individual neural pulses (spikes) in biological neural\nsystems, it is crucial for memristive synapses to support the\nspike-time-dependent plasticity (STDP), which is believed to be the primary\nmechanism of Hebbian adaptation. A major challenge for the STDP implementation\nis that, in contrast to some simplistic models of the plasticity, the\nelementary change of a synaptic weight in an artificial hardware synapse\ndepends not only on the pre-synaptic and post-synaptic signals, but also on the\ninitial weight (memristor's conductance) value. Here we experimentally\ndemonstrate, for the first time, STDP protocols that ensure self-adaptation of\nthe average memristor conductance, making the plasticity stable, i.e.\ninsensitive to the initial state of the devices. The experiments have been\ncarried out with 200-nm Al2O3/TiO2-x memristors integrated into 12x12\ncrossbars. The experimentally observed self-adaptive STDP behavior has been\ncomplemented with numerical modeling of weight dynamics in a simple system with\na leaky-integrate-and-fire neuron with a random spike-train input, using a\ncompact model of memristor plasticity, fitted for quantitatively correct\ndescription of our memristors.", "category": "cond-mat_other" }, { "text": "Fr\u00f6hlich Polarons. Lecture course including detailed theoretical\n derivations -- 10th edition: In the present course, an overview is presented of the fundamentals of\ncontinuum-polaron physics, which provide the basis of the analysis of polaron\neffects in ionic crystals and polar semiconductors. These Lecture Notes deal\nwith \"large\", or \"continuum\", polarons, as described by the Fr\\\"ohlich\nHamiltonian. The emphasis is on the polaron optical absorption, with detailed\nmathematical derivations.", "category": "cond-mat_other" }, { "text": "Self-sustained Levitation of Dust Aggregate Ensembles by Temperature\n Gradient Induced Overpressures: In laboratory experiments we observe dust aggregates from 100 \\mu m to 1 cm\nin size composed of micrometer sized grains levitating over a hot surface.\nDepending on the dust sample aggregates start to levitate at a temperature of\n400 K. Levitation of dust aggregates is restricted to a pressure range between\n1--40 mbar. The levitating is caused by a Knudsen compressor effect. Based on\nthermal transpiration through the dust aggregates the pressure increases\nbetween surface and aggregates. Dust aggregates are typically balanced 100 \\mu\nm over the surface. On a slightly concave surface individual aggregates are\ntrapped at the center. Ensembles of aggregates are confined in a 2D plane.\nAggregates are subject to systematic and random translational and rotational\nmotion. The levitated aggregates are well suited to study photophoretic or\nthermophoretic forces on dust aggregates or the mutual interaction between dust\naggregates.", "category": "cond-mat_other" }, { "text": "Nonlinear tunneling of BEC in an optical lattice: signatures of quantum\n collapse and revival: Quantum theory of the intraband resonant tunneling of a Bose-Einstein\ncondensate loaded in a twodimensional optical lattice is considered. It is\nshown that the phenomena of quantum collapse and revival can be observed in the\nfully quantum problem. The mean-field limit of the theory is analyzed using the\nWKB approximation for discrete equations, establishing in this way a direct\nconnection between the two approaches conventionally used in very different\nphysical contexts. More specifically we show that there exist two different\nregimes of tunneling and study dependence of quantum collapse and revival on\nthe number of condensed atoms.", "category": "cond-mat_other" }, { "text": "Dynamic Tsallis entropy for simple model systems: In this paper we consider the dynamic Tsallis entropy and employ it for four\nmodel systems: (i) the motion of Brownian oscillator, (ii) the motion of\nBrownian oscillator with noise, (iii) the fluctuation of particle density in\nhydrodynamics limit as well as in (iv) ideal gas. We show that the small value\nof parameter nonextensivity $0=|1,1>$ hyperfine states. The\nresonances appear as trap losses for the $^7$Li cloud induced by inelastic\nheteronuclear three-body collisions. The magnetic field values where they occur\nare important quantities for an accurate determination of the interspecies\ninteraction potentials. Results of coupled channels calculations based on the\nobserved resonances are presented and refined potential parameters are given. A\nvery broad Feshbach resonance centered around 649 G should allow for fine\ntuning of the interaction strength in future experiments.", "category": "cond-mat_other" }, { "text": "Accurate measurement of ^{13}C - ^{15}N distances with solid-state NMR: Solid-state NMR technique for measureing distances between hetero-nuclei in\nstatic powder samples is described. It is based on a two-dimensional\nsingle-echo scheme enhanced with adiabatic cross-polarization. As an example,\nthe results for intra-molecular distances in $\\alpha$-crystalline form of\nglycine are presented. The measured NMR distances ^13 C(2) - ^15 N and ^13 C(1)\n- ^15 N are 1.496 $\\pm$ 0.002 \\AA and 2.50 $\\pm$ 0.02 \\AA, respectively.", "category": "cond-mat_other" }, { "text": "Theory of ground states for classical Heisenberg spin systems IV: We extend the theory of ground states of classical Heisenberg spin systems\npreviously published to the case where the interaction with an external\nmagnetic field is described by a Zeeman term. The ground state problem for the\nHeisenberg-Zeeman Hamiltonian can be reduced first to the relative ground state\nproblem, and, in a second step, to the absolute ground state problem for pure\nHeisenberg Hamiltonians depending on an additional Lagrange parameter. We\ndistinguish between continuous and discontinuous reduction. Moreover, there are\nvarious general statements about Heisenberg-Zeeman systems that will be proven\nunder most general assumptions. One topic is the connection between the minimal\nenergy functions $E_{min}$ for the Heisenberg energy and $H_{min}$ for the\nHeisenberg-Zeeman energy which turn out to be essentially mutual\nLegendre-Fenchel transforms. This generalization of the traditional Legendre\ntransform is especially suited to cope with situations where the function\n$E_{min}$ is not convex and consequently there is a magnetization jump at a\ncritical field. Another topic is magnetization and the occurrence of threshold\nfields $B_{thr}$ and saturation fields $B_{sat}$, where we provide a general\nformula for the latter. We suggest a distinction between ferromagnetic and\nanti-ferromagnetic systems based on the vanishing of $B_{sat}$ for the former\nones. Parabolic systems are defined in such a way that $E_{min}$ and $H_{min}$\nhave a particularly simple form and studied in detail. For a large class of\nparabolic systems the relative ground states can be constructed from the\nabsolute ground state by means of a so-called umbrella family. Finally we\nprovide a counter-example of a parabolic system where this construction is not\npossible.", "category": "cond-mat_other" }, { "text": "Macroscopic quantum tunnelling of Bose-Einstein condensates in a finite\n potential well: Bose-Einstein condensates are studied in a potential of finite depth which\nsupports both bound and quasi-bound states. This potential, which is harmonic\nfor small radii and decays as a Gaussian for large radii, models experimentally\nrelevant optical traps. The nonlinearity, which is proportional to both the\nnumber of atoms and the interaction strength, can transform bound states into\nquasi-bound ones. The latter have a finite lifetime due to tunnelling through\nthe barriers at the borders of the well. We predict the lifetime and stability\nproperties for repulsive and attractive condensates in one, two, and three\ndimensions, for both the ground state and excited soliton and vortex states. We\nshow, via a combination of the variational and WKB approximations, that\nmacroscopic quantum tunnelling in such systems can be observed on time scales\nof 10 milliseconds to 10 seconds.", "category": "cond-mat_other" }, { "text": "Thomas-Fermi versus one- and two-dimensional regimes of a trapped\n dipolar Bose-Einstein condensate: We derive the criteria for the Thomas-Fermi regime of a dipolar Bose-Einstein\ncondensate in cigar, pancake and spherical geometries. This also naturally\ngives the criteria for the mean-field one- and two-dimensional regimes. Our\npredictions, including the Thomas-Fermi density profiles, are shown to be in\nexcellent agreement with numerical solutions. Importantly, the anisotropy of\nthe interactions has a profound effect on the Thomas-Fermi/low-dimensional\ncriteria.", "category": "cond-mat_other" }, { "text": "Controlled quantum stirring of Bose-Einstein condensates: By cyclic adiabatic change of two control parameters of an optical trap one\ncan induce a circulating current of condensed bosons. The amount of particles\nthat are transported per period depends on the \"radius\" of the cycle, and this\ndependence can be utilized in order to probe the interatomic interactions. For\nstrong repulsive interaction the current can be regarded as arising from a\nsequence of Landau-Zener crossings. For weaker interaction one observes either\ngradual or coherent mega crossings, while for attractive interaction the\nparticles are glued together and behave like a classical ball. For the analysis\nwe use the Kubo approach to quantum pumping with the associated Dirac monopoles\npicture of parameter space.", "category": "cond-mat_other" }, { "text": "An exploration of thermal counterflow in He II using particle tracking\n velocimetry: Visualization of thermal counterflow in He II using PIV (particle image\nvelocimetry) and PTV (particle tracking velocimetry) is difficult because\ntracer particle motion can be influenced by both the normal fluid and\nsuperfluid components of He II as well as the quantized vortex tangle. For\ninstance, an early PTV experiment observed particles moving at the normal fluid\nvelocity $v_n$, while a PIV experiment observed particles moving at $v_n/2$,\nthough the range of heat flux applied in these experiments differed by an order\nof magnitude. To resolve this apparent discrepancy and explore statistics of\nparticle motion in thermal counterflow, we have applied PTV to a wide range of\nheat flux at several fluid temperatures. We introduce a scheme for analyzing\nthe velocity of particles presumably moving with the normal fluid separately\nfrom those presumably influenced by the vortex tangle. Our results show two\ndistinct peaks in the streamwise particle velocity PDF (probability density\nfunction) for lower heat flux, one centered at the normal fluid velocity $v_n$\n(\"G2\") and one near $v_n/2$ (\"G1\"). For higher heat flux there is a single peak\ncentered near $v_n/2$ (\"G3\"). Using our separation scheme we show there is no\nsize difference between particles contributing to G1 and G2. We also show that\nnon-classical features of the transverse velocity PDF arise entirely from G1,\nwhile the corresponding PDF for G2 exhibits classical Gaussian form. G2\ntransverse velocity fluctuation, backed up by second sound attenuation in\ndecaying counterflow, suggests large scale turbulence in the normal fluid is\nabsent from the two peak region. We offer a brief discussion of physical\nmechanisms that may be responsible for our observations, revealing that G1\nvelocity fluctuations may be linked to fluctuations of vortex line velocity,\nand suggest numerical simulations that may reveal underlying physics in detail.", "category": "cond-mat_other" }, { "text": "Exact Coulomb cutoff technique for supercell calculations in two\n dimensions: We present a reciprocal space technique for the calculation of the Coulomb\nintegral in two dimensions in systems with reduced periodicity, i.e., finite\nsystems, or systems that are periodic only in one dimension. The technique\nconsists in cutting off the long-range part of the interaction by modifying the\nexpression for the Coulomb operator in reciprocal space. The physical result\namounts in an effective screening of the spurious interactions originated by\nthe presence of ghost periodic replicas of the system. This work extends a\nprevious report [C. A. Rozzi et al., Phys. Rev. B 73, 205119 (2006)], where\nthree-dimensional systems were considered. We show that the use of the cutoffs\ndramatically enhances the accuracy of the calculations for a given supercell\nsize, and it allows to describe two-dimensional systems of reduced periodicity\nwith substantially less computational effort. In particular, we consider\nsemiconductor quantum-dot arrays having potential applications in quantum\ninformation technology.", "category": "cond-mat_other" }, { "text": "Photoconduction in Alq3: Photoelectronic properties of Alq3 were studied by photoconductivity\nmeasurements in thin film, sandwich (ITO/Alq3/LiF/Al) devices. We find that the\nphotocurrent is dominated by bulk generation of carriers for incident photon\nenergies greater than 2.75 eV. The quantum efficiency of photocarrier\ngeneration has been measured from carrier collection measurements to be about\n10%. The quantum efficiency is largely independent of electric field. This\nenables a direct measurement of the electric field dependence of mobility using\nphotoconductivity measurements, which is used for quantitative analysis of the\ndark forward current in these devices. Photoconductivity measurements were also\nused to obtain (\\mu_{0n} \\tau_n) product which can be used as a measure of\nmaterial quality. For Alq3, we find that the value of (\\mu_{0n} \\tau_n) product\nwas between 3x10^{-15} cm^2/V to 8x10^{-15} cm^2/V for different samples. In\nforward bias, at high field the photocurrent shows saturation accompanied by a\nphase shift. These effects are attributed to space charge effects in the\ndevice.", "category": "cond-mat_other" }, { "text": "Emergent Time Scale in Entangled Quantum Dynamics of Ultracold Molecules\n in Optical Lattices: We derive a novel lattice Hamiltonian, the \\emph{Molecular Hubbard\nHamiltonian} (MHH), which describes the essential many body physics of\nclosed-shell ultracold heteronuclear molecules in their absolute ground state\nin a quasi-one-dimensional optical lattice. The MHH is explicitly\ntime-dependent, making a dynamic generalization of the concept of quantum phase\ntransitions necessary. Using the Time-Evolving Block Decimation (TEBD)\nalgorithm to study entangled dynamics, we demonstrate that, in the case of hard\ncore bosonic molecules at half filling, the MHH exhibits an emergent time scale\nover which spatial entanglement grows, crystalline order appears, and\noscillations between rotational states self-damp into an asymptotic\nsuperposition. We show that this time scale is a non-monotonic function of the\nphysical parameters describing the lattice. We also point out that experimental\nmapping of the static phase boundaries of the MHH can be used to measure the\nmolecular polarizability tensor.", "category": "cond-mat_other" }, { "text": "Disorder, defects and bandgaps in ultra thin (001) MgO tunnel barrier\n layers: We report scanning tunneling spectroscopy studies of the electronic structure\nof 1.5 to 3 nm (001) textured MgO layers grown on (001) Fe. Thick MgO layers\nexhibit a bulk-like band gap, approximately 5-7 eV, and sparse, localized\ndefect states with characteristics attributable to oxygen and, in some cases,\nMg vacancies. Thin MgO layers exhibit electronic structure indicative of\ninteracting defect states forming band tails which in the thinnest case extend\nto approximately 0.5 V of the Fermi level. These vacancy defects are ascribed\nto compressive strain from the MgO/Fe lattice mismatch, accommodated as the MgO\ngrows.", "category": "cond-mat_other" }, { "text": "Electrical spin injection into p-doped quantum dots through a tunnel\n barrier: We have demonstrated by electroluminescence the injection of spin polarized\nelectrons through Co/Al2O3/GaAs tunnel barrier into p-doped InAs/GaAs quantum\ndots embedded in a PIN GaAs light emitting diode. The spin relaxation processes\nin the p-doped quantum dots are characterized independently by optical\nmeasurements (time and polarization resolved photoluminescence). The measured\nelectroluminescence circular polarization is about 15 % at low temperature in a\n2T magnetic field, leading to an estimation of the electrical spin injection\nyield of 35%. Moreover, this electroluminescence circular polarization is\nstable up to 70 K.", "category": "cond-mat_other" }, { "text": "Viscoelastic Behavior of Solid $^4$He: Over the last five years several experimental groups have reported anomalies\nin the temperature dependence of the period and amplitude of a torsional\noscillator containing solid $^4$He. We model these experiments by assuming that\n$^4$He is a viscoelastic solid--a solid with frequency dependent internal\nfriction. We find that while our model can provide a quantitative account of\nthe dissipation observed in the torsional oscillator experiments, it only\naccounts for about 10% of the observed period shift, leaving open the\npossibility that the remaining period shift is due to the onset of\nsuperfluidity in the sample.", "category": "cond-mat_other" }, { "text": "Conservative-dissipative forces and heating mediated by fluctuation\n electromagnetic field: two plates in relative nonrelativistic motion: We calculate heating rate, attractive conservative and tangential dissipative\nfluctuation electromagnetic forces felt by a thick plate moving with\nnonrelativistic velocity parallel to a closely spaced another plate in rest\nusing relativistic fluctuation electrodynamics. We argue that recently\ndeveloped relativistic out of equilibrium theory of fluctuation electromagnetic\ninteractions (Volokitin et. al., Phys.Rev. B78, 155437 (2008))has serious\ndrawbacks.", "category": "cond-mat_other" }, { "text": "Wealth distribution in an ancient Egyptian society: Modern excavations yielded a distribution of the house areas in the ancient\nEgyptian city Akhetaten, which was populated for a short period during the 14th\ncentury BC. Assuming that the house area is a measure of the wealth of its\ninhabitants allows us to make a comparison of the wealth distributions in\nancient and modern societies.", "category": "cond-mat_other" }, { "text": "Basic theory tools for degenerate Fermi gases: This is an introductory lecture to the theory of degenerate Fermi gases, in\nthe context of present experiments on atomic Fermi gases. In part one, some\nproperties of the ideal Fermi gas are presented, including a discussion of the\nfluctuations of the number of fermions in a given spatial zone in 1D, 2D and\n3D. In part two, two-body aspects of the interaction potential are discussed\nand several possible models for the interaction are analyzed, including the\ntwo-channel model for the Feshbach resonance. In part three, basic predictions\nof zero temperature BCS theory are presented, including a derivation of\nsuperfluid hydrodynamic equations from time dependent BCS theory.", "category": "cond-mat_other" }, { "text": "The surface-forming energy release rate based fracture criterion for\n elastic-plastic crack propagation: J integral based criterion is widely used in elastic-plastic fracture\nmechanics. However, it is not rigorously applicable when plastic unloading\nappears during crack propagation. One difficulty is that the energy density\nwith plastic unloading in J integral cannot be defined unambiguously. In this\npaper, we alternatively start from the analysis on the power balance, and\npropose a surface-forming energy release rate (ERR), which represents the\nenergy directly dissipated on the surface-forming during the crack propagation\nand excludes the loading-mode-dependent plastic dissipation. Therefore the\nsurface-forming ERR based fracture criterion has wider applicability, including\nelastic-plastic crack propagation problems. Several formulae have been derived\nfor calculating the surface-forming ERR. From the most concise formula, it is\ninteresting to note that the surface-forming ERR can be computed only by the\nstress and deformation of the current moment, and the definition of the energy\ndensity or work density is avoided. When an infinitesimal contour is chosen,\nthe expression can be further simplified. For any fracture behaviors, the\nsurface-forming ERR is proven to be path-independent, and the path-independence\nof its constituent term, so-called integral, is also investigated. The physical\nmeanings and applicability of the proposed surface-forming ERR, traditional\nERR, Js integral and J integral are compared and discussed.", "category": "cond-mat_other" }, { "text": "Discrete symmetry in graphene: the Dirac equation and beyond: In this pedagogical paper we review the discrete symmetries of the Dirac\nequation using elementary tools, but in a comparative order: the usual 3 + 1\ndimensional case and the 2 + 1 dimensional case. Motivated by new applications\nof the 2d Dirac equation in condensed matter, we further analyze the discrete\nsymmetries of a full tight-binding model in hexagonal lattices without conical\napproximations. We touch upon an effective CPT symmetry breaking that occurs\nwhen deformations and second-neighbor corrections are considered.", "category": "cond-mat_other" }, { "text": "Collective Excitations of a Two-Component Bose Condensate at Finite\n Temperature: We compare the collective modes for Bose-condensed systems with two\ndegenerate components with and without spontaneous intercomponent coherence at\nfinite temperature using the time-dependent Hartree-Fock approximation. We show\nthat the interaction between the condensate and non-condensate in these two\ncases results in qualitatively different collective excitation spectra. We show\nthat at zero temperature the single-particle excitations of the incoherent Bose\ncondensate can be probed by intercomponent excitations.", "category": "cond-mat_other" }, { "text": "Material independent crack arrest statistics: The propagation of (planar) cracks in a heterogeneous brittle material\ncharacterized by a random field of toughness is considered, taking into account\nexplicitly the effect of the crack front roughness on the local stress\nintensity factor. In the so-called strong-pinning regime, the onset of crack\npropagation appears to map onto a second-order phase transition characterized\nby universal critical exponents which are independent of the local\ncharacteristics of the medium. Propagation over large distances can be\ndescribed by using a simple one-dimensional description, with a correlation\nlength and an effective macroscopic toughness distribution that scale in a\nnon-trivial fashion with the crack front length. As an application of the above\nconcepts, the arrest of indentation cracks is addressed, and the analytical\nexpression for the statistical distribution of the crack radius at arrest is\nderived. The analysis of indentation crack radii on alumina is shown to obey\nthe predicted algebraic expression for the radius distribution and its\ndependence on the indentation load.", "category": "cond-mat_other" } ]