Impurity-controlled vortex mobility and pair-breaking in fermionic superfluid rings

TL;DR

This study uses density functional theory to explore how impurity characteristics affect vortex mobility and dissipation in fermionic superfluid rings, revealing impurity-dependent regimes and pair-breaking effects.

Contribution

It introduces a detailed analysis of impurity-controlled vortex dynamics and dissipation mechanisms in fermionic superfluids, with implications for ultracold atoms and neutron-star physics.

Findings

Critical winding number increases with impurity density

Impurity size influences vortex emission and pinning regimes

Flow energy dissipates via impurity-enhanced pair-breaking

Abstract

Using time-dependent density functional theory, we study how density and size of impurities govern dissipation of persistent currents of fermionic superfluid rings in the BCS regime. The critical winding number for vortex emission increases with impurity density, but this enhancement is impurity size-dependent and capped by the pair-breaking threshold. Below this vortex-emission threshold, the winding number remains constant while flow energy dissipates through impurity-enhanced pair-breaking. Above the threshold, vortex-impurity interactions produce distinct mobility regimes-deflected trajectories, individual pinning, collective pinning, and inter-site hopping, controlled by the impurity size and density, which determine the dominant dissipation channel. These findings provide design principles for ultracold-atom experiments and insights into vortex-pinning dynamics in neutron-star crusts and superconductors.