Metallic phase in the two-dimensional ionic Hubbard model

TL;DR

This study uses determinant quantum Monte Carlo to explore the phase diagram of the two-dimensional ionic Hubbard model, revealing Mott, band insulators, and a metallic phase at the crossover, with antiferromagnetism confined to the Mott region.

Contribution

First comprehensive quantum Monte Carlo analysis of the 2D ionic Hubbard model identifying distinct insulating and metallic phases.

Findings

Mott and band insulators at strong interactions or potentials

Metallic phase appears when energies are comparable

Antiferromagnetism only in the Mott insulating region

Abstract

We investigate the phases of the ionic Hubbard model in a two-dimensional square lattice using determinant quantum Monte Carlo (DQMC). At half-filling, when the interaction strength or the staggered potential dominate we find Mott and band insulators, respectively. When these two energies are of the same order we find a metallic region. Charge and magnetic structure factors demonstrate the presence of antiferromagnetism only in the Mott region, although the externally imposed density modulation is present everywhere in the phase diagram. Away from half-filling, other insulating phases are found. Kinetic energy correlations do not give clear signals for the existence of a bond-ordered phase.