Quantum-spin-Hall insulator with a large gap: single-layer 1T' WSe$_2$

TL;DR

This paper reports the growth and characterization of a large-gap 2D topological insulator in single-layer 1T' WSe2, demonstrating its potential for room-temperature spintronic applications.

Contribution

The study presents the first experimental realization of a large-gap 2D topological insulator in single-layer 1T' WSe2 with tunable electronic properties.

Findings

Observed a 129 meV band gap in 1T' WSe2 via ARPES and STM/STS.

Detected in-gap edge states near the layer boundary.

Doping with Rb reduces the gap, leading to an insulator-semimetal transition.

Abstract

Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum spin Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe$_2$ single layer with the 1T' structure that does not exist in the bulk form of WSe$_2$. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observed a gap of 129 meV in the 1T' layer and an in-gap edge state located near the layer boundary. The system's 2D TI characters are confirmed by first-principles calculations. The observed gap diminishes with doping by Rb adsorption, ultimately leading to an insulator-semimetal transition. The discovery of this large-gap 2D TI with a tunable band gap opens up opportunities for developing advanced nanoscale systems and quantum devices.