Realization of Quantum Spin Hall State in Monolayer 1T'-WTe2

TL;DR

This paper demonstrates that monolayer 1T'-WTe2 exhibits a quantum spin Hall state characterized by topological band inversion, a sizable band gap, and edge states, confirmed through ARPES, STM, and first-principles calculations.

Contribution

It provides the first experimental evidence of a QSH state in monolayer 1T'-WTe2, a transition metal dichalcogenide, highlighting its potential as a robust 2D topological insulator.

Findings

Observation of topological band inversion in monolayer 1T'-WTe2

Confirmation of a sizable bulk band gap via STM

Detection of edge states consistent with QSH insulator

Abstract

A quantum spin Hall (QSH) insulator is a novel two-dimensional quantum state of matter that features quantized Hall conductance in the absence of magnetic field, resulting from topologically protected dissipationless edge states that bridge the energy gap opened by band inversion and strong spin-orbit coupling. By investigating electronic structure of epitaxially grown monolayer 1T'-WTe2 using angle-resolved photoemission (ARPES) and first principle calculations, we observe clear signatures of the topological band inversion and the band gap opening, which are the hallmarks of a QSH state. Scanning tunneling microscopy measurements further confirm the correct crystal structure and the existence of a bulk band gap, and provide evidence for a modified electronic structure near the edge that is consistent with the expectations for a QSH insulator. Our results establish monolayer 1T'-WTe2 as a new class of QSH insulator with large band gap in a robust two-dimensional materials family of transition metal dichalcogenides (TMDCs).