Dark solitons in a superfluid Fermi gas

TL;DR

This paper explores the properties of dark solitons in a superfluid Fermi gas across the BCS-BEC crossover, revealing how soliton density profiles and superfluid gaps change with interaction strength.

Contribution

It provides a detailed analysis of dark solitons using Bogoliubov-de Gennes equations, highlighting differences in soliton behavior across the crossover and the impact of Andreev bound states.

Findings

Deep density minima in the unitary region

Superfluid gap quenched by solitons due to bound states

Distinct soliton profiles in different regimes

Abstract

We investigate the behavior of dark solitons in a superfluid Fermi gas along the BCS-BEC crossover by solving the Bogoliubov - de Gennes equations and looking for real and odd solutions for the order parameter. We show that in the resonance unitary region, where the scattering length is large, the density profile of the soliton has a deep minimum, differently from what happens in the BCS regime. The superfluid gap is found to be significantly quenched by the presence of the soliton due to the occurrence of Andreev fermionic bound states localized near the nodal plane of the order parameter.