title: Correlated insulated phase suggests bond order between band and mott insulators in two dimensions.
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 Delta, the so-called ionic Hubbard model, using cluster dynamical mean-field theory. We find that for large Coulomb repulsion, U >> Delta, the system is a Mott insulator (MI). For weak to intermediate values of Delta, on decreasing U, the Mott gap closes at a critical value Uc1(Delta) beyond which a correlated insulating phase with possible bond order is found. Further, this phase undergoes a first-order transition to a band insulator (BI) at Uc2(Delta) with a finite charge gap at the transition. For large Delta, there is a direct first-order transition from a MI to a BI with a single metallic point at the phase boundary.
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 32831, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Kancharla
authors.forename: E
authors.initials: E
authors.lastname: Dagotto