BCS-BEC crossover in an asymmetric two-component Fermi gas

TL;DR

This paper investigates the superfluid phase transition in an asymmetric two-component Fermi gas near the BCS-BEC crossover, analyzing phase stability and critical chemical potential differences with fluctuation effects included.

Contribution

It provides a phase diagram for asymmetric Fermi gases near the BCS-BEC crossover, incorporating fluctuation effects of preformed pairs and identifying conditions for different superfluid phases.

Findings

Normal gas becomes unstable below a critical chemical potential difference.

Identification of conditions favoring Fulde-Ferrell-Larkin-Ovchinnikov or uniform superfluid phases.

Qualitative agreement with experimental measurements of critical chemical potential mismatch.

Abstract

We discuss the superfluid phase transition of a strongly interacting Fermi gas with unequal (asymmetric) chemical potentials in two pairing hyperfine states, and map out its phase diagram near the BCS-BEC crossover. Our approach includes the fluctuation contributions of {}``preformed Cooper pairs'' to the thermodynamic potential at finite temperature. We show that, below a critical difference in chemical potentials between species, a normal gas is unstable towards the formation of either a finite-momentum paired Fulde-Ferrell-Larkin-Ovchinnikov superconducting phase or a uniform superfluid, depending on the asymmetry and interaction strengths. We determine the value of critical chemical potential mismatch, and find good qualitative agreement with a recent measurement by Zwierlein \textit{et al.} {[}Science \textbf{311}, 492 (2006){]}.