Superfluid-density of the ultra-cold Fermi gas in optical lattices

TL;DR

This paper investigates the superfluid density in an ultra-cold Fermi gas within optical lattices, comparing different phases including BCS, FFLO, and Sarma, and analyzing their stability and superfluid properties.

Contribution

It provides a comparative analysis of superfluid densities across BCS, FFLO, and Sarma phases in imbalanced Fermi gases, highlighting the stability of the FFLO phase under certain conditions.

Findings

FFLO superfluid density differs significantly from BCS/Sarma.

FFLO phase is stable at weak coupling and high densities.

Dynamical instabilities are present in FFLO at strong coupling.

Abstract

In this paper we study the superfluid density of the two component Fermi gas in optical lattices with population imbalance. Three different type of phases, the BCS-state (Bardeen, Cooper, and Schrieffer), the FFLO-state (Fulde, Ferrel, Larkin, and Ovchinnikov), and the Sarma state, are considered. We show that the FFLO superfluid density differs from the BCS/Sarma superfluid density in an important way. Although there are dynamical instabilities in the FFLO phase, when the interaction is strong or densities are high, on the weak coupling limit the FFLO phase is found to be stable.