Leggett collective excitations in a two-band Fermi superfluid at finite temperatures

Abstract

The Leggett collective excitations for a two-band Fermi gas with s-wave pairing and Josephson interband coupling in the BCS-BEC crossover at finite temperatures are investigated within the Gaussian pair fluctuation approach. Eigenfrequencies and damping factors for Leggett modes are determined in a nonperturbative way, using the analytic continuation of the fluctuation propagator through a branch cut in the complex frequency plane, as in Phys. Rev. Lett. 122, 093403 (2019). The treatment is performed beyond the low-energy expansion, which is necessary when the collective excitation energy reaches the pair-breaking continuum edge. The results are applied in particular to cold atomic gases at the orbital Feshbach resonance and in a regime far from BEC, which can be relevant for future experiments.

11 pages, 5 figures

References in corpus (7)

• Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
• Observation of Leggett's collective mode in a multi-band MgB2 superconductor
• Two-band superfluidity from the BCS to the BEC limit
• Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC crossover in a two-band Fermi gas
• Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas
• Phase separation in imbalanced fermion superfluids beyond mean-field
• Two-band description of resonant superfluidity in atomic Fermi gases

Cited by in corpus (6)

• Following the Higgs mode across the BCS-BEC crossover in two dimensions
• Mechanism of screening or enhancing the pseudogap throughout the two-band Bardeen-Cooper-Schrieffer to Bose-Einstein condensate crossover
• Collective excitations of a BCS superfluid in the presence of two sublattices
• Dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance across the phase transition from BCS to Sarma superfluid
• Superfluid properties of an ultracold Fermi gas with an orbital Feshbach resonance in the BCS-BEC crossover region
• Two-band atomic superfluidity in the presence of an orbital Feshbach resonance