Proximity Enhanced Quantum Spin Hall State in Graphene

TL;DR

This paper predicts a significant proximity-induced enhancement of the quantum spin Hall energy gap in graphene sandwiched between certain materials, making it experimentally observable and controllable, thus advancing the study of topological insulators.

Contribution

It introduces a novel method to induce a sizable QSH gap in graphene via proximity effects with Sb2Te3 or MoTe2, enabling experimental detection of the QSH effect.

Findings

Proximity effect increases the QSH gap in graphene by three orders of magnitude.

The enhanced gap (1.5 meV) is accessible with current experimental techniques.

The QSH state is driven by the Kane-Mele interaction, tunable by interlayer distance.

Abstract

Graphene is the first model system of two-dimensional topological insulator (TI), also known as quantum spin Hall (QSH) insulator. The QSH effect in graphene, however, has eluded direct experimental detection because of its extremely small energy gap due to the weak spin-orbit coupling. Here we predict by ab initio calculations a giant (three orders of magnitude) proximity induced enhancement of the TI energy gap in the graphene layer that is sandwiched between thin slabs of Sb2Te3 (or MoTe2). This gap (1.5 meV) is accessible by existing experimental techniques, and it can be further enhanced by tuning the interlayer distance via compression. We reveal by a tight-binding study that the QSH state in graphene is driven by the Kane-Mele interaction in competition with Kekul\'e deformation and symmetry breaking. The present work identifies a new family of graphene-based TIs with an observable and controllable bulk energy gap in the graphene layer, thus opening a new avenue for direct verification and exploration of the long-sought QSH effect in graphene.