Exitonic Excitation of a Superfluid Fermi Gas in a Double-layer Optical Lattice

We study the phase diagram and the collective excitations of an attractive two-component Fermi gas on a doubl-layer optical lattice at zero temperature. The introduction of one-particle hopping term between the two layers generates many more interesting phenomena, including the superfluid-insulator transition and a new excitonic-like excitations. We characterize the phase transitions and investigate in detail the properties of excitonic excitations, including its gap and effective mass.