Bogoliubov Theory for a Superfluid Bose Gas Flowing in a Random Potential: Stability and Critical Velocity

TL;DR

This paper uses Bogoliubov theory to analyze the stability and critical velocity of a superfluid Bose gas flowing through a disordered potential, revealing how disorder, flow velocity, and temperature affect superfluid properties.

Contribution

It introduces a method to determine condensate and superfluid densities in disordered systems with flow, and calculates the critical velocity considering system size effects in two dimensions.

Findings

Critical velocity depends on disorder strength, flow velocity, and temperature.

In two dimensions, the critical velocity is strongly size-dependent.

The spectrum of hydrodynamic excitations determines flow stability.

Abstract

We investigate the stability and critical velocity of a weakly interacting Bose gas flowing in a random potential. By applying the Bogoliubov theory to a disordered Bose system with a steady flow, the condensate density and the superfluid density are determined as functions of the disorder strength, flow velocity, and temperature. The critical velocity, at which the steady flow becomes unstable, is calculated from the spectrum of hydrodynamic excitation. We also show that in two dimensions the critical velocity strongly depends on the system size.