Physics – Condensed Matter – Soft Condensed Matter
Scientific paper
2002-01-15
Physics
Condensed Matter
Soft Condensed Matter
12 pages, 3 figures
Scientific paper
10.1103/PhysRevLett.89.130402
We discuss the BCS-BEC crossover in a degenerate Fermi gas of two hyperfine states interacting close to a Feshbach resonance. This system has quasi-molecular Bosons associated with a Feshbach resonance, and this kinds of coupled Boson-Fermion model has been recently applied to Fermi atomic gases within a mean-field approximation. We show that by including fluctuation contribution to the free energy similar to that condiered by Nozi'eres and Schmitt-Rink, the character of the superfluid phase transition continuously changes from the BCS-type to the BEC-type, as the threshold of the quasi-molecular band is lowered. In the BEC regime, the quasi-molecules become stable long-lived composite Bosons, and an effective pairing interaction mediated by the molecules causes pre-formed Cooper-pairs to also be stable even above the transition temperature Tc. The superfluid phase transition is shown to be usefully interpreted as the Bose condensation of these two kinds of Bosons. The maximum Tc is given by (in terms of the Fermi temperature T_F) Tc=0.218T_F (uniform gas) and Tc=0.518T_F (trapped gas in a harmonic potential).
Griffin Allan
Ohashi Yoji
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