Supercurrent Stability in a Quasi-1D Weakly Interacting Bose Gas

We discuss a possibility of observing superfluid phenomena in a quasi-1D weakly interacting Bose gas at finite temperatures. The weakness of interaction in combination with generic properties of 1D liquids can result in a situation when relaxational time of supercurrent is essentially larger than the time of experimental observation, and the behavior of the system is indistinguishable from that of a genuine superfluid.Comment: Revtex, 4 pages, no figures; Submitted to Phys. Rev. A (Brief Reports

Calculation of the microcanonical temperature for the classical Bose field

The ergodic hypothesis asserts that a classical mechanical system will in time visit every available configuration in phase space. Thus, for an ergodic system, an ensemble average of a thermodynamic quantity can equally well be calculated by a time average over a sufficiently long period of dynamical evolution. In this paper we describe in detail how to calculate the temperature and chemical potential from the dynamics of a microcanonical classical field, using the particular example of the classical modes of a Bose-condensed gas. The accurate determination of these thermodynamics quantities is essential in measuring the shift of the critical temperature of a Bose gas due to non-perturbative many-body effects.Comment: revtex4, 10 pages, 1 figure. v2: updated to published version. Fuller discussion of numerical results, correction of some minor error

Critical Dynamics of a Two-dimensional Superfluid near a Non-Thermal Fixed Point

Critical dynamics of an ultracold Bose gas far from equilibrium is studied in two spatial dimensions. Superfluid turbulence is created by quenching the equilibrium state close to zero temperature. Instead of immediately re-thermalizing, the system approaches a meta-stable transient state, characterized as a non-thermal fixed point. A focus is set on the vortex density and vortex-antivortex correlations which characterize the evolution towards the non-thermal fixed point and the departure to final (quasi-)condensation. Two distinct power-law regimes in the vortex-density decay are found and discussed in terms of a vortex binding-unbinding transition and a kinetic description of vortex scattering. A possible relation to decaying turbulence in classical fluids is pointed out. By comparing the results to equilibrium studies of a two-dimensional Bose gas, an intuitive understanding of the location of the non-thermal fixed point in a reduced phase space is developed.Comment: 11 pages, 13 figures; PRA versio

Exact Results for Three-Body Correlations in a Degenerate One-Dimensional Bose Gas

Motivated by recent experiments we derive an exact expression for the correlation function entering the three-body recombination rate for a one-dimensional gas of interacting bosons. The answer, given in terms of two thermodynamic parameters of the Lieb-Liniger model, is valid for all values of the dimensionless coupling $\gamma$ and contains the previously known results for the Bogoliubov and Tonks-Girardeau regimes as limiting cases. We also investigate finite-size effects by calculating the correlation function for small systems of 3, 4, 5 and 6 particles.Comment: 4 pages, 2 figure

Condensation and vortex formation in Bose-gas upon cooling

The mechanism for the transition of a Bose gas to the superfluid state via thermal fluctuations is considered. It is shown that in the process of external cooling some critical fluctuations (instantons) are formed above the critical temperature. The probability of the instanton formation is calculated in the three and two-dimensional cases. It is found that this probability increases as the system approaches the transition temperature. It is shown that the evolution of an individual instanton is impossible without the formation of vortices in its superfluid part

Sound attenuation in the superconducting amorphous alloy ZrTiCuNiBe

The superconducting energy gap and the parameter of the intensity of electron scattering at two-level systems in amorphous ZrTiCuNiBe are determined from the results of measurements of sound attenuation. The mechanism of adiabatic renormalization of the amplitude of coherent tunneling is used for a quantitative description of the peculiarities of sound absorption in the vicinity of critical temperature.Comment: 4 pages, LaTeX, 2 Postscript figures corrected, submitted to Low Temp. Phy

Rayleigh-Taylor instability of crystallization waves at the superfluid-solid 4He interface

At the superfluid-solid 4He interface there exist crystallization waves having much in common with gravitational-capillary waves at the interface between two normal fluids. The Rayleigh-Taylor instability is an instability of the interface which can be realized when the lighter fluid is propelling the heavier one. We investigate here the analogues of the Rayleigh-Taylor instability for the superfluid-solid 4He interface. In the case of a uniformly accelerated interface the instability occurs only for a growing solid phase when the magnitude of the acceleration exceeds some critical value independent of the surface stiffness. For the Richtmyer-Meshkov limiting case of an impulsively accelerated interface, the onset of instability does not depend on the sign of the interface acceleration. In both cases the effect of crystallization wave damping is to reduce the perturbation growth-rate of the Taylor unstable interface.Comment: 8 pages, 2 figures, RevTe

Modeling of the M2 surface and internal tides and their seasonal variability in the Arctic Ocean: Dynamics, energetics and tidally induced diapycnal diffusion

Modeling results for the M2 surface and internal tides in the Arctic Ocean (AO) are presented. These incorporate the data on tidal dynamics and energetics and tidally induced diapycnal diffusion. A modified version of the 3D finite-element hydrostatic model QUODDY-4 is used as a basis for modeling. It is shown that the predicted surface tide differs slightly from that obtained from other tidal models, whereas the internal tidal waves (ITW) are less than those in oceans of moderate and low latitudes. It also appears that ITW themselves belong to the family of trapped waves. This finding, together with the modeling results for averaged (over a tidal cycle) horizontal transport per unit length of barotropic tidal energy and depth-integrated density of baroclinic tidal energy, suggests that the ITW generation site is placed to the northwest of the New Siberian Islands. A local rate of baroclinic tidal energy dissipation is found to increase away from the bottom as observed on Mid-Atlantic and Hawaiian ridges, but only within the bottom boundary layer, and two-three orders of magnitude less than in other oceans. Also, the ITW decay scale in both summer and winter lies over the range of its values (100–1000 km) for Mid-Atlantic and Hawaiian ridges. A tidal cycle-, depth- and area-averaged coefficient of diapycnal diffusion is greater than the kinematic viscosity and less (but not much) than the canonical value of the vertical eddy diffusivity in the deep ocean, prescribed in models of global ocean circulation. From this results the conclusion that tidally induced diapycnal diffusion can be meaningful in the formation of the AO climate

On the theory of pseudogap anisotropy in the cuprate superconductors

We show by means of the theory of the order parameter phase fluctuations that the temperature of "closing" (or "opening") of the gap (and pseudogap) in the electron spectra of superconductors with anisotropic order parameter takes place within a finite temperature range. Every Fourier-component of the order parameter has its own critical temperature