Subsonic critical velocity at finite temperature

TL;DR

This paper extends the dielectric formalism to finite temperature Bose gases, showing that the critical velocity is lower than the sound velocity due to thermal effects, highlighting differences from zero-temperature models.

Contribution

It introduces a dynamic method to determine the critical velocity at finite temperature within the dielectric formalism framework.

Findings

Critical velocity at finite temperature is lower than the sound velocity.

The model distinguishes between conserving and gapless approximations.

Finite temperature effects influence the stability transition in Bose gases.

Abstract

Based on the dielectric formalism in the generalised random phase approximation, we generalise the description of a Bose condensed gas to allow for a relative velocity between the superfluid and normal fluid. In this model, we determine the critical velocity dynamically as the transition point between stable and unstable dynamics. Unlike the zero temperature case, at finite temperature the relative critical velocity of a dilute Bose gas is lower than the sound velocity. This result illustrates one relevant difference that exists between a conserving and gapless approximation and other approaches.