Interaction-driven Band-insulator--to--Metal transition in bilayer ionic Hubbard model

TL;DR

This study investigates how interlayer hybridization and phase relations of ionic potentials influence the insulator-metal transition in a bilayer ionic Hubbard model, revealing that in-phase potentials expand the metallic phase.

Contribution

It introduces a bilayer extension of the ionic Hubbard model and shows that in-phase ionic potentials enlarge the interaction-driven metallic phase.

Findings

In-phase ionic potentials expand the metallic phase in the phase diagram.

Anti-phase potentials always lead to insulating states with charge order.

The results suggest possible extensions to three-dimensional models.

Abstract

The interaction-driven insulator-to-metal transition has been reported in the ionic Hubbard model (IHM) for moderate interaction $U$, while its metallic phase only occupies a narrow region in the phase diagram. To explore the enlargement of the metallic regime, we extend the ionic Hubbard model to two coupled layers and study the interplay of interlayer hybridization $V$ and two types of intralayer staggered potentials $\Delta$: one with the same (in-phase) and the other with a $\pi$-phase shift (anti-phase) potential between layers. Our determinant Quantum Monte Carlo (DQMC) simulations at lowest accessible temperatures demonstrate that the interaction-driven metallic phase between Mott and band insulators expands in the $\Delta-V$ phase diagram of bilayer IHM only for in-phase ionic potentials; while anti-phase potential always induces an insulator with charge density order. This implies possible further extension of the ionic Hubbard model from the bilayer case here to realistic three-dimensional model.