Bose-Einstein-condensed gases in arbitrarily strong random potentials

TL;DR

This paper develops a stochastic mean-field approach to study Bose-Einstein condensates in strong random potentials, revealing complex interactions between condensate, superfluid, and glassy densities across various interaction and disorder strengths.

Contribution

It introduces a comprehensive theoretical framework that captures the effects of arbitrarily strong disorder and interactions on Bose-Einstein condensates, including phase transitions and coexistence phenomena.

Findings

Superfluid fraction can be smaller than condensate fraction at weak interactions and strong disorder.

Condensate and superfluid fractions coexist, being either both nonzero or both zero.

Disorder induces a first-order phase transition leading to a sudden collapse of condensate and superfluid fractions.

Abstract

Bose-Einstein-condensed gases in external spatially random potentials are considered in the frame of a stochastic self-consistent mean-field approach. This method permits the treatment of the system properties for the whole range of the interaction strength, from zero to infinity, as well as for arbitrarily strong disorder. Besides a condensate and superfluid density, a glassy number density due to a spatially inhomogeneous component of the condensate occurs. For very weak interactions and sufficiently strong disorder, the superfluid fraction can become smaller than the condensate fraction, while at relatively strong interactions, the superfluid fraction is larger than the condensate fraction for any strength of disorder. The condensate and superfluid fractions, and the glassy fraction always coexist, being together either nonzero or zero. In the presence of disorder, the condensate fraction becomes a nonmonotonic function of the interaction strength, displaying an antidepletion effect caused by the competition between the stabilizing role of the atomic interaction and the destabilizing role of the disorder. With increasing disorder, the condensate and superfluid fractions jump to zero at a critical value of the disorder parameter by a first-order phase transition.