Europhys. Lett., 75 (3), pp. 364-370 (2006)
DOI: 10.1209/epl/i2006-10136-3

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

Xia-Ji Liu¹ and Hui Hu<sup>1, 2

1</sup>  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 in final form 19 June 2006
published online 5 July 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).

PACS
03.75.Hh - Static properties of condensates; thermodynamical, statistical and structural properties.
03.75.Ss - Degenerate Fermi gases.
05.30.Fk - Fermion systems and electron gas.

© EDP Sciences 2006

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