Disorder effects during the evolution from BCS to BEC superfluidity

TL;DR

This paper investigates how disorder influences the critical temperature of superfluids across the BCS-BEC crossover, revealing that disorder impacts phase coherence differently depending on the regime, with superfluid robustness varying along the transition.

Contribution

It provides a detailed analysis of disorder effects on superfluid critical temperature during the BCS to BEC evolution, highlighting differences in pair breaking and phase coherence.

Findings

Disorder has minimal effect on critical temperature in the BCS regime.

In the BEC regime, disorder significantly reduces critical temperature by affecting phase coherence.

Superfluid robustness against weak disorder peaks in the intermediate regime.

Abstract

We describe the effects of disorder on the critical temperature of s-wave superfluids from the BCS to the BEC regime, with direct application to ultracold Fermi atoms. In the BCS regime the pair breaking and phase coherence temperature scales are essentially the same allowing strong correlations between the amplitude and phase of the order parameter. As non-pair breaking disorder is introduced the largely overlapping Cooper pairs conspire to maintain phase coherence such that the critical temperature remains essentially unchanged. However, in the BEC regime the pair breaking and phase coherence temperature scales are very different such that non-pair breaking disorder can affect dramatically phase coherence, and thus the critical temperature, without the requirement of breaking tightly-bound fermion pairs simultaneously. Finally, we find that the superfluid is more robust against weak disorder in the intermediate region between the two regimes.