Resonant superfluidity in an optical lattice

We have studied a system of ultracold fermionic potassium (40K) atoms in a three-dimensional (3D) optical lattice in the vicinity of an s-wave Feshbach resonance. Close to resonance, the system is described by a multi-band Bose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian in which the effect of higher bands is incorporated by a self-consistent mean-field approximation. The resulting model is solved by means of generalized dynamical mean-field theory. In addition to the BEC-BCS crossover, we find a phase transition to a fermionic Mott insulator at half-filling, induced by the repulsive fermionic background scattering length. We also calculate the critical temperature of the BEC/BCS state and find it to be minimal at resonance