The two-dimensional topological insulators (2DTI) host a full gap in the bulk band, induced by spin-orbit coupling (SOC) effect, together with the topologically protected gapless edge states. However, the SOC-induced gap is usually small, and it is challenging to suppress the bulk conductance and thus to realize the quantum spin Hall (QSH) effect. In this study, we find a novel mechanism to effectively suppress the bulk conductance. By using the quasiparticle interference (QPI) technique with scanning tunneling spectroscopy (STS), we demonstrate that the QSH candidate single-layer 1T'-WTe2 has a semi-metal bulk band structure with no full SOC-induced gap. Surprisingly, in this two-dimensional system, we find the 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 is in favor of the observation of the quantized conduction of topological edge states.
@article{arxiv.1711.07286,
title = {Observation of Coulomb gap in the quantum spin Hall candidate single-layer 1T'-WTe$_2$},
author = {Ye-Heng Song and Zhen-Yu Jia and Dongqin Zhang and Xin-Yang Zhu and Zhi-Qiang Shi and Huaiqiang Wang and Li Zhu and Qian-Qian Yuan and Haijun Zhang and Dingyu Xing and Shao-Chun Li},
journal= {arXiv preprint arXiv:1711.07286},
year = {2018}
}