Buried topological edge state associated with interface between topological band insulator and Mott insulator

TL;DR

This study investigates the interface between a topological band insulator and a Mott insulator, revealing a buried topological edge state and a novel proximity effect influenced by spin-orbit coupling.

Contribution

It demonstrates a new type of proximity effect where the edge state amplitude peaks within the Mott insulator and shows phase conversion near the interface due to spin-orbit interactions.

Findings

Edge state is metallic and peaks inside the Mott insulator near critical Coulomb energy.

Layer conversion from Mott insulator to topological insulator occurs near the interface.

A reverse proximity effect enhances the density of states in the metallic layer.

Abstract

The electronic structure at the interface between a topological band insulator and a Mott insulator is studied within layer dynamical mean field theory. To represent the bulk phases of these systems, we use the generalized Bernevig-Hughes-Zhang model that incorporates the Hubbard-like onsite Coulomb energy U in addition to the spin-orbit coupling term that causes band inversion. The topological and Mott insulating phases are realized by appropriately choosing smaller and larger values of U, respectively. As expected, the interface is found to be metallic because of the localized edge state. When the Coulomb energy in the Mott insulator is close to the critical value, however, this edge state exhibits its largest amplitude deep within the Mott insulator rather than at the interface. This finding corresponds to a new type of proximity effect induced by the neighboring topological band insulator and demonstrates that, as a result of spin-orbit coupling within the Mott insulator, several layers near the interface convert from the Mott insulating phase to a topological insulating phase. Moreover, we argue that the ordinary proximity effect, whereby a Kondo peak is induced in a Mott insulator by neighboring metallic states, is accompanied by an additional reverse proximity effect, by which the Kondo peak gives rise to an enhancement of the density of states in the neighboring metallic layer.