  The superfluid-insulator transitions of the fermionic atoms in optical
lattices are investigated by the two-site dynamical mean-field theory. It is
shown that the Mott transition occurs as a result of the multiband effects. The
quasiparticle weight in the superfluid state decreases significantly, as the
system approaches the Mott transition point. By changing the interaction and
the orbital splitting, we obtain the phase diagram at half filling. The
numerical results are discussed in comparison with the effective boson model.
