Multiband-driven superfluid-insulator transition of fermionic atoms in optical lattices: A dynamical mean-field-theory study

The superfluid-insulator transition of fermionic atoms in optical lattices is investigated by two-site dynamical mean-field theory. It is shown that the Mott transition occurs as a result of 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.

Figure 1

(Color online) Quasiparticle weight $Z$, superfluid order parameter $\Phi$, and filling of each band $n_1,n_2$ for $U^{\prime }=J=U/2$. The DOSs of the lowest band are shown in the right panels of (a) and (b). The results show three types of transitions: (a) the transition between the superfluid and the Mott insulator, (b) the transition between the superfluid and the band insulator, and (c) the transition between the band insulator and the Mott insulator.

Figure 2

(Color online) Phase diagram for $U^{\prime }=J=U/2$ at half filling. On the attractive side the bosonic fermion pair occupies either of the two orbitals at each site, while on the repulsive side the fermionic atoms occupy both orbitals at each site.

Figure 3

(Color online) Superfluid order parameter $\Phi$ and quasiparticle weight $Z$ as functions of the attractive interaction $U$ for several values of $J$ at $U^{\prime }=U/2$ and $D=0$.