Critical velocity of a finite-temperature Bose gas

TL;DR

This paper investigates how finite temperature affects the critical velocity for superfluid breakdown in a Bose gas, revealing that thermal fluctuations lower the vortex nucleation threshold and alter vortex structures.

Contribution

It provides a detailed analysis of vortex nucleation mechanisms at finite temperature using classical field simulations, highlighting the temperature dependence of critical velocity.

Findings

Critical velocity decreases with increasing temperature.

Vortex structures evolve from lines to rings and tangles with temperature.

Critical velocity approaches zero at the Bose-Einstein condensation temperature.

Abstract

We use classical field simulations of the homogeneous Bose gas to study the breakdown of superflow due to vortex nucleation past a cylindrical obstacle at finite temperature. Thermal fluctuations modify the vortex nucleation from the obstacle, turning anti-parallel vortex lines (which would be nucleated at zero temperature) into wiggly lines, vortex rings and even vortex tangles. We find that the critical velocity for vortex nucleation decreases with increasing temperature, and scales with the speed of sound of the condensate, becoming zero at the critical temperature for condensation.