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

¹ ARC Centre of Excellence for Quantum-Atom Optics, Department of Physics University of Queensland - Brisbane, Queensland 4072, Australia
² Department of Physics, Renmin University of China - Beijing 100872, PRC

Received: 11 April 2006
Accepted: 19 June 2006

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 that it is consistent with a recent measurement by Zwierlein et al.  (Science, 311 (2006) 492).