Quantum Phase transition in the two dimensional ionic-Hubbard model

TL;DR

This paper investigates how the ionic potential affects the phase transitions in the two-dimensional Hubbard model, revealing a transition from band insulator to metal and then to Mott insulator phases using dynamical mean field theory.

Contribution

It introduces a detailed analysis of phase transitions in the ionic-Hubbard model on a square lattice, highlighting the competition between ionic potential and electron interactions.

Findings

Identification of a metallic intermediate phase between band insulator and Mott insulator.

Demonstration that increasing Hubbard U can close and reopen the energy gap.

Mapping of phase boundaries as a function of U and ionic potential Δ.

Abstract

We employ the dynamical mean field approximation to study the effects of ionic potential ($\Delta$) on the square lattice Hubbard model. At half-filling when the staggered potential ($\Delta$) dominates the on-site Hubbard interaction ($U$), the system is in the band insulator phase. We find that competition between $U$ and $\Delta$ 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 $U\leq 9t$ and $\Delta\approx 0$ the phase of the system is metallic, but for larger $U$ the system is in the Mott insulator phase.