Stability of persistent currents in superfluid fermionic rings

Abstract

We investigate the stability of persistent currents in superfluid fermionic gases confined to a ring geometry. Our study, conducted at zero temperature using time-dependent density functional theory, cover interaction regimes from strong (unitary Fermi gas) to weak (Bardeen-Cooper-Schrieffer regime) couplings. Stability is tested against the presence of an external defect within the ring. The dissipation mechanism associated with vortex generation is present in all interaction regimes. Vortex emission is accompanied by Cooper pair breaking, which occurs even beyond the vortex core in the weakly interacting regime. The pair-breaking mechanism prevents the imprinting of a persistent current with a winding number above a threshold, which decreases as the system approach the BCS regime. Our study reveals the existence of two types of critical winding numbers above which currents cease to be persistent in Fermi superfluids: one related to the proliferation of quantum vortices and the other to the onset of the pair-breaking mechanism.