Quantum phase transitions in the two dimensional ionic-Hubbard model

Abstract

We employ the dynamical mean field approximation to study the effects of ionic potential (Δ) on the square lattice Hubbard model. At half-filling when the staggered potential (Δ) dominates the on-site Hubbard interaction (U), the system is in the band insulator phase. We find that competition between U and Δ can suppress the gap to zero and leading to an intermediate metallic region. At the large-U limit, we identify a Mott insulator phase where the gap opens again and increases upon increasing the Hubbard interaction U. For U ≤ 9t and Δ ≈ 0 the phase of the system is metallic, but for larger U the system is in the Mott insulator phase.