Resonant pair-exchange scattering and BCS-BEC crossover in a system composed of dispersive and heavy incipient bands: A Feshbach analogy

We theoretically show that a two-band system with very different masses harbors resonant pair scattering leads to novel pairing properties, as highlighted by the Bardeen-Cooper-Schrieffer (BCS) Bose-Einstein condensation (BEC) crossover. Most importantly, interband pair-exchange coupling induces an effective intraband attraction in each band, enhancing superfluidity/superconductivity. The effect, kind of Suhl-Kondo mechanism, is specifically enhanced when second band has heavy mass and incipient (lying close to, but just above, chemical potential $\ensuremath{\mu}$), which we call scattering. By elucidating dependence interactions gap functions on $\ensuremath{\mu}$, can draw analogy between Feshbach resonance.