Population and mass imbalance in atomic Fermi gases

TL;DR

This paper develops a precise theoretical framework for resonantly interacting Fermi mixtures with spin and mass imbalance, focusing on the ${}^{6}$Li-${}^{40}$K mixture, and uncovers a Lifshitz point indicating potential supersolid phases.

Contribution

It provides the first detailed phase diagram for mass-imbalanced Fermi mixtures at various interaction strengths, including the universal unitarity regime.

Findings

Identifies a Lifshitz point in the phase diagram for large mass imbalances.

Predicts an instability towards a supersolid phase in certain conditions.

Provides phase diagrams relevant for experimental ${}^{6}$Li-${}^{40}$K} mixture studies.

Abstract

We develop an accurate theory of resonantly interacting Fermi mixtures with both spin and mass imbalance. We consider Fermi mixtures with arbitrary mass imbalances, but focus in particular on the experimentally available ${}^{6}$Li-${}^{40}$K mixture. We determine the phase diagram of the mixture for different interactions strengths that lie on the BCS side of the Feshbach resonance. We also determine the universal phase diagram at unitarity. We find for the mixtures with a sufficiently large mass imbalance, that includes the ${}^{6}$Li-${}^{40}$K mixture, a Lifshitz point in the universal phase diagram that signals an instability towards a supersolid phase.