Gutzwiller approximation for paramagnetic ionic Hubbard model: Analytic expression for band-Mott insulator transition

TL;DR

This paper derives an analytic expression for the phase boundary between Mott and band insulators in the ionic Hubbard model using the Gutzwiller approximation, clarifying the method's capabilities and limitations.

Contribution

It provides a compact analytic formula for the phase transition in the ionic Hubbard model within the Gutzwiller approximation, highlighting its strengths and limitations.

Findings

Reproduces band-Mott insulator phenomenology

Does not capture correlated metallic state at finite staggered potential

Establishes a variational framework for the ionic Hubbard model

Abstract

The ionic Hubbard model is a paradigmatic setup for studying the competition between band and Mott insulating behavior. Within the variationally exact in infinite dimensions Gutzwiller approximation, we derive a compact analytic expression for the phase boundary between Mott and band insulator. While the method reproduces the expected band-Mott insulator phenomenology, it does not capture the correlated metallic state at finite staggered potential found for example in dynamical mean-field theory. This absence highlights that the metallic phase originates from incoherent Hubbard-band physics rather than Fermi-liquid behavior well captured by Gutzwiller approximation. Our formulation establishes a concise variational framework to ionic Hubbard model, with natural extensions to nonequilibrium setups and spin-exchange dynamics.