Superfluid phase transition and strong-coupling effects in an ultracold Fermi gas with mass imbalance

TL;DR

This paper studies how mass imbalance influences the superfluid transition in ultracold Fermi gases, extending existing theories to accurately describe strong-coupling effects and providing insights relevant to various superfluid systems.

Contribution

The authors extend the T-matrix theory to include higher-order pairing fluctuations to accurately analyze superfluid transitions in mass-imbalanced Fermi gases.

Findings

Mass imbalance significantly affects the superfluid transition temperature.

Standard Gaussian fluctuation and T-matrix theories give unphysical results with mass imbalance.

The extended T-matrix theory provides more reliable predictions for superfluid properties.

Abstract

We investigate the superfluid phase transition and effects of mass imbalance in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an cold Fermi gas. We point out that the Gaussian fluctuation theory developed by Nozi\`eres and Schmitt-Rink and the $T$-matrix theory, that are now widely used to study strong-coupling physics of cold Fermi gases, give unphysical results in the presence of mass imbalance. To overcome this problem, we extend the $T$-matrix theory to include higher-order pairing fluctuations. Using this, we examine how the mass imbalance affects the superfluid phase transition. Since the mass imbalance is an important key in various Fermi superfluids, such as $^{40}$K-$^6$Li Fermi gas mixture, exciton condensate, and color superconductivity in a dense quark matter, our results would be useful for the study of these recently developing superfluid systems.