Superfluidity of electron-hole pairs in randomly inhomogeneous bilayer systems

In bilayer systems electron-hole (e-h) pairs with spatially separated components (i.e., with electrons in one layer and holes in the other) can be condensed to a superfluid state when the temperature is lowered. This article deals with the influence of randomly distributed inhomogeneities on the superfluid properties of such bilayer systems in a strong perpendicular magnetic field. Ionized impurities and roughenings of the conducting layers are shown to decrease the superfluid current density of the e-h pairs. When the interlayer distance is smaller than or close to the magnetic length, the fluctuations of the interlayer distance considerably reduce the superfluid transition temperature.Comment: 13 pages, 3 figure

Relaxation of superflow in a network: an application to the dislocation model of supersolidity of helium crystals

We have considered the dislocation network model for the supersolid state in He-4 crystals. In difference with uniform 2D and 3D systems, the temperature of superfluid transition T_c in the network is much smaller than the degeneracy temperature T_d. It is shown that a crossover into a quasi superfluid state occurs in the temperature interval between T_c and T_d. Below the crossover temperature the time of decay of the flow increases exponentially under decrease of the temperature. The crossover has a continuous character and the crossover temperature does not depend on the density of dislocations.Comment: Corrected typo

Quenched Dislocation Enhanced Supersolid Ordering

I show using Landau theory that quenched dislocations can facilitate the supersolid (SS) to normal solid (NS) transition, making it possible for the transition to occur even if it does not in a dislocation-free crystal. I make detailed predictions for the dependence of the SS to NS transition temperature T_c(L), superfluid density %\rho_S(T, L), and specific heat C(T,L) on temperature T and dislocation spacing L, all of which can be tested against experiments. The results should also be applicable to an enormous variety of other systems, including, e.g., ferromagnets.Comment: 5 pages, 2 figure

Vortex matter and generalizations of dipolar superfluidity concept in layered systems

In the first part of this letter we discuss electrodynamics of an excitonic condensate in a bilayer. We show that under certain conditions the system has a dominant energy scale and is described by the effective electrodynamics with "planar magnetic charges". In the second part of the paper we point out that a vortex liquid state in bilayer superconductors also possesses dipolar superfluid modes and establish equivalence mapping between this state and a dipolar excitonic condensate. We point out that a vortex liquid state in an N-layer superconductor possesses multiple topologically coupled dipolar superfluid modes and therefore represents a generalization of the dipolar superfluidity concept.Comment: v2: references added. v3: discussion extended, references adde

Dynamic equation for quantum Hall bilayers with spontaneous interlayer coherence: The low-density limit

The bilayer systems exhibit the Bose-Einstein condensation of excitons that emerge due to Coulomb pairing of electrons belonging to one layer with the holes belonging to the other layer. Here we present the microscopic derivation of the dynamic equation for the condensate wave function at a low density of electron-hole ($e-h$) pairs in a strong magnetic field perpendicular to the layers and an electric field directed along the layers. From this equation we obtain the dispersion law for collective excitations of the condensate and calculate the electric charge of the vortex in the exciton condensate. The critical interlayer spacing, the excess of which leads to a collapse of the superfluid state, is estimated. In bilayer systems with curved conducting layers, the effective mass of the $e-h$ pair becomes the function of the $e-h$ pair coordinates, the regions arise, where the energy of the $e-h$ pair is lowered (exciton traps), and lastly $e-h$ pairs can gain the polarization in the basal plane. This polarization leads to the appearance of quantized vortices even at zero temperature.Comment: 8 page

Superfluid to Bose-glass transition in a 1D weakly interacting Bose gas

We study the one-dimensional Bose gas in spatially correlated disorder at zero temperature, using an extended density-phase Bogoliubov method. We analyze in particular the decay of the one-body density matrix and the behaviour of the Bogoliubov excitations across the phase boundary. We observe that the transition to the Bose glass phase is marked by a power-law divergence of the density of states at low energy. A measure of the localization length displays a power-law energy dependence in both regions, with the exponent equal to -1 at the boundary. We draw the phase diagram of the superfluid-insulator transition in the limit of small interaction strength.Comment: 4 pages, 4 figure

Fluid Models for Kinetic Effects on Coherent Nonlinear Alfven Waves. II. Numerical Solutions

The influence of various kinetic effects (e.g. Landau damping, diffusive and collisional dissipation, and finite Larmor radius terms) on the nonlinear evolution of finite amplitude Alfvenic wave trains in a finite-beta environment is systematically investigated using a novel, kinetic nonlinear Schrodinger (KNLS) equation. The dynamics of Alfven waves is sensitive to the sense of polarization as well as the angle of propagation with respect to the ambient magnetic field. Numerical solution for the case with Landau damping reveals the formation of dissipative structures, which are quasi-stationary, S-polarized directional (and rotational) discontinuities which self-organize from parallel propagating, linearly polarized waves. Parallel propagating circularly polarized packets evolve to a few circularly polarized Alfven harmonics on large scales. Stationary arc-polarized rotational discontinuities form from obliquely propagating waves. Collisional dissipation, even if weak, introduces enhanced wave damping when beta is very close to unity. Cyclotron motion effects on resonant particle interactions introduce cyclotron resonance into the nonlinear Alfven wave dynamics.Comment: 38 pages (including 23 figures and 1 table

The dynamics of dark solitons in a trapped superfluid Fermi gas

We study soliton oscillations in a trapped superfluid Fermi gas across the Bose-Einstein condensate to Bardeen-Cooper-Schrieffer (BEC-BCS) crossover. We derive an exact equation relating the phase jump across the soliton to its energy, and hence obtain an expression for the soliton period. Our analytic approach is supported by simulations of the time-dependent Bogoliubov-de Gennes equations, which show that the period dramatically increases as the soliton becomes shallower on the BCS side of the resonance. Finally, we propose an experimental protocol to test our predictions.Comment: 5 pages, 4 figure