Abstract
We investigate the ground state phase diagram of the half-filled repulsive Hubbard model in two dimensions in the presence of a staggered potential ?, the so-called ionic Hubbard model, using cluster dynamical mean field theory. We find that for large Coulomb repulsion, U �� , the system
is a Mott insulator (MI). For weak to intermediate values of ?, on decreasing U, the Mott gap closes at a critical value Uc1(?) beyond which a correlated insulating phase with possible bond order (BO) is found. Further, this phase undergoes a first-order transition to a band insulator (BI) at Uc2(?)
with a finite charge gap at the transition. For large ?, there is a direct first-order transition from a MI to a BI with a single metallic point at the phase boundary
