Phase diagrams of Fermi gases in a trap with mass and population imbalances at finite temperature

TL;DR

This paper presents finite-temperature phase diagrams of mass- and population-imbalanced Fermi gases, revealing exotic phase separation and shell structures, especially in $^{6}$Li--$^{40}$K mixtures, using a pairing fluctuation theory.

Contribution

It provides new phase diagrams and identifies novel shell structures in imbalanced Fermi gases at finite temperature and trap effects, focusing on $^{6}$Li--$^{40}$K mixtures.

Findings

Existence of exotic phase separation in the BEC regime.

Sandwich-like shell structures with superfluid or pseudogapped normal states.

Shell structures become prominent with increased mass imbalance.

Abstract

The pairing and superfluid phenomena in a two-component Fermi gas can be strongly affected by the population and mass imbalances. Here we present phase diagrams of atomic Fermi gases as they undergo BCS--Bose-Einstein condensation (BEC) crossover with population and mass imbalances, using a pairing fluctuation theory. We focus on the finite temperature and trap effects, with an emphasis on the mixture of $^{6}$Li and $^{40}$K atoms. We show that there exist exotic types of phase separation in the BEC regime as well as sandwich-like shell structures at low temperature with superfluid or pseudogapped normal state in the central shell in the BCS and unitary regimes, especially when the light species is the majority. Such a sandwich-like shell structure appear when the mass imbalance increases beyond certain threshold. Our result is relevant to future experiments on the $^6$Li--$^{40}$K mixture and possibly other Fermi-Fermi mixtures.