Finite-Temperature Behavior of an Inter-species Fermionic Superfluid with Population Imbalance

TL;DR

This paper investigates the finite-temperature phase diagram and superfluid transition temperature of an inter-species fermionic mixture with population imbalance, revealing the potential for experimental observation of superfluid phases.

Contribution

It provides the first comprehensive phase diagram for a heteronuclear fermionic mixture across the BCS-BEC crossover with population imbalance, including effects of pairing fluctuations.

Findings

Superfluid transition temperature $T_c$ is significantly reduced from pairing onset temperature $T^*$.

Inter-species superfluid phase is experimentally accessible.

Generalized-Sarma phase appears as an intermediate-temperature superfluid.

Abstract

We determine the superfluid transition temperature $T_c$ and related finite temperature phase diagrams for the entire BCS-Bose Einstein condensation crossover in a homogeneous mixture of $^{6}$Li and $^{40}$K atoms with population imbalance. Our work is motivated by the recent observation of an inter-species Feshbach resonance. Pairing fluctuation effects, which significantly reduce $T_c$ from the onset temperature for pairing ($T^*$), provide reasonable estimates of $T_c$ and indicate that the inter-species superfluid phase should be accessible in future experiments. Although a generalized-Sarma phase is not stable in the ground state near unitarity, our phase diagrams show that it appears as an intermediate-temperature superfluid.