Stability of the Breached Pair State for a Two-species Fermionic System in the Presence of Feshbach Resonance

Abstract

We investigate the phenomenon of fermionic pairing with mismatched Fermi surfaces in a two-species system in the presence of Feshbach resonance, where the resonantly-paired fermions combine to form bosonic molecules. We observe that the Feshbach parameters control the critical temperature of the gapped BCS superfluid state, and also determine the range over which a gapless breached pair state may exist. Demanding the positivity of the superfluid density, it is shown that although a breached pair state with two Fermi surfaces is always unstable, its single Fermi-surface counterpart can be stable if the chemical potentials of the two pairing species have opposite signs. This condition is satisfied only over a narrow region in the BEC side, characterized by an upper and a lower limit for the magnetic field. We estimate these limits for a mixture of two hyperfine states of ${}^6$Li using recent experimental data.

14 pages,5 figures

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Cited by in corpus (2)

• Dimensional Crossover in a Spin-imbalanced Fermi gas
• Effects of three-body scattering processes on BCS-BEC crossover