Two-fluid model for a rotating trapped Fermi gas in the BCS phase

TL;DR

This paper studies the dynamical response of a trapped Fermi gas in the BCS superfluid phase to slow rotation, revealing a significant normal-fluid component at low temperatures that complicates experimental detection of superfluidity.

Contribution

It introduces a two-fluid model with a position-dependent normal and superfluid density ratio to describe the gas's response to rotation in the BCS phase.

Findings

Normal-fluid component appears in outer regions at low temperatures

Rotation induces currents explained by the two-fluid model

Superfluid effects are harder to observe experimentally

Abstract

We investigate the dynamical properties of a superfluid gas of trapped fermionic atoms in the BCS phase. As a simple example we consider the reaction of the gas to a slow rotation of the trap. It is shown that the currents generated by the rotation can be understood within a two-fluid model similar to the one used in the theory of superconductors, but with a position dependent ratio of normal and superfluid densities. The rather general result of this paper is that already at very low temperatures, far below the critical one, an important normal-fluid component appears in the outer regions of the gas. This renders the experimental observation of superfluidity effects more difficult and indicates that reliable theoretical predictions concerning other dynamical properties, like the frequencies of collective modes, can only be made by taking into account temperature effects.