Observation of Coulomb gap in the quantum spin Hall candidate single-layer 1T\u2019-WTe2

Ye-Heng Song,Huaiqiang Wang,Haijun Zhang,Ding-Yu Xing,Shao-Chun Li,Zhi-Qiang Shi,Qian-Qian Yuan,Zhen-Yu Jia,Dongqin Zhang,Xin-Yang Zhu,Li Zhu

doi:10.1038/s41467-018-06635-x

Abstract

The two-dimensional topological insulators host a full gap in the bulk band, induced by spin–orbit coupling (SOC) effect, together with the topologically protected gapless edge states. However, it is usually challenging to suppress the bulk conductance and thus to realize the quantum spin Hall (QSH) effect. In this study, we find a mechanism to effectively suppress the bulk conductance. By using the quasiparticle interference technique with scanning tunneling spectroscopy, we demonstrate that the QSH candidate single-layer 1T’-WTe2 has a semimetal bulk band structure with no full SOC-induced gap. Surprisingly, in this two-dimensional system, we find the electron–electron interactions open a Coulomb gap which is always pinned at the Fermi energy (EF). The opening of the Coulomb gap can efficiently diminish the bulk state at the EF and supports the observation of the quantized conduction of topological edge states.

Highlights

The two-dimensional topological insulators host a full gap in the bulk band, induced by spin–orbit coupling (SOC) effect, together with the topologically protected gapless edge states
Qian et al.[11] predicted a class of quantum spin Hall (QSH) materials in the single-layer 1T’-phase of transition-metal dichalcogenide (TMD), TX2, where T represents a transition-metal atom (Mo, W) and X stands for a chalcogen atom (S, Se, or Te)
The band inversion happens between transition-metal d orbitals and chalcogenide p orbitals, and the SOC interaction further opens a fundamental band gap[11]

Summary

Introduction

The two-dimensional topological insulators host a full gap in the bulk band, induced by spin–orbit coupling (SOC) effect, together with the topologically protected gapless edge states. By using the quasiparticle interference technique with scanning tunneling spectroscopy, we demonstrate that the QSH candidate single-layer 1T’WTe2 has a semimetal bulk band structure with no full SOC-induced gap. In this two-dimensional system, we find the electron–electron interactions open a Coulomb gap which is always pinned at the Fermi energy (EF). Unlike the SOC-induced gap, as generally considered in 2DTIs, the Coulomb gap discovered in this study always locates at the Fermi level, independent of the electron doping This exotic gap in the singlelayer 1T’-WTe2 can efficiently filter its topological edge channels directly from the vanishing bulk states at the Fermi level, regardless of the gap size

Methods

Results

Conclusion