Critical velocity, vortex shedding and drag in a unitary Fermi superfluid

TL;DR

This paper investigates how a microscopic object moves through a unitary Fermi superfluid, revealing vortex creation at a critical velocity and analyzing the resulting drag forces in different motion regimes.

Contribution

It introduces an extended Thomas-Fermi density functional approach to study vortex shedding and drag in a unitary Fermi superfluid, highlighting the transition from linear to quadratic drag.

Findings

Vortex-antivortex pairs are spontaneously created above a critical velocity.

Drag force is linear in velocity for subsonic motion.

Drag force becomes quadratic in velocity for supersonic motion.

Abstract

We study the real-time motion of a microscopic object in a cold Fermi gas at unitary conditions by using an extended Thomas-Fermi density functional approach. We find that spontaneous creation of singly quantized vortex-antivortex pairs occurs as a critical velocity is exceeded, which leads to a drag between the moving object and the Fermi gas. The resulting force is linear in the velocity for subsonic motion and becomes quadratic for supersonic motion.