Superfluid stability in BEC-BCS crossover

TL;DR

This paper investigates the stability of superfluid phases in a two-species fermionic gas across the BEC-BCS crossover, revealing conditions for stability and phase transitions influenced by unbound fermions and coupling strength.

Contribution

It provides a theoretical analysis of superfluid stability in fermionic gases with unequal concentrations, identifying critical coupling thresholds and phase transition mechanisms.

Findings

Uniform superfluid is stable only beyond a critical coupling or at weak coupling.

System exhibits a transition from superfluid to normal Fermi gas.

Distinct properties arise due to unbound fermions near Feshbach resonance.

Abstract

We consider a dilute atomic gas of two species of fermions with unequal concentrations under a Feshbach resonance. We find that the system can have distinct properties due to the unbound fermions. The uniform state is stable only when either (a) beyond a critical coupling strength, where it is a gapless superfluid, or (b) when the coupling strength is sufficiently weak, where it is a normal Fermi gas mixture. Phase transition(s) must therefore occur when the resonance is crossed.