Mott insulator to superfluid transition of ultracold bosons in an optical lattice near a Feshbach resonance

We study the phase diagram of ultracold bosons in an optical lattice near a Feshbach resonance. Depending on the boson density, the strength of the optical lattice potential and the detuning from resonance, the ground state can be a Mott insulator, a superfluid phase with both an atomic and a molecular condensate, or a superfluid phase with only a molecular condensate. Mott insulator to superfluid transitions can be induced either by decreasing the strength of the optical lattice potential or by varying the detuning from the Feshbach resonance. Quite generally, we find that for a commensurate density the ground-state may undergo several insulator-superfluid or superfluid-insulator transitions as the magnetic field is varied through the resonance.