Abstract
The quantum spin Hall (QSH) effect is widely studied as a novel quantum state in condensed matter physics over the past decade. Recently, it is predicted that the transition metal pentatelluride XTe5 (X = Zr, Hf) has a large bandgap in its bulk form and a single layer of XTe5 is a QSH insulator candidate. However, the topological nature of the bulk material is still under debate because it is located close to the phase boundary of a strong topological insulator and a weak topological insulator (WTI). Here, using angle-resolved photoemission spectroscopy and scanning tunneling microscopy (STM)/scanning tunneling spectroscopy, we systematically studied the electronic structures of bulk HfTe5. Both the large bulk bandgaps and conductive edge states in the vicinity of the step edges in HfTe5 were observed, strongly suggesting a WTI phase in bulk HfTe5. Moreover, our STM experiment for the first time reveals the bulk band bending due to the broken symmetry near the step edge, making it an ideal platform for studying the development of edge states in the WTI and QSH insulator.
Highlights
Quantum Spin Hall (QSH) insulators are quantum materials with a bulk insulating gap and helical transport channels at the edge protected by time reversal symmetry (TRS) without backscattering,[1,2,3,4] making them good candidates for dissipationless transport
Starting from HgTe/CdTe and InAs/GaSb heterostructures[2,4,5,6] to monolayer stanene[7,8,9,10] and 1T’-transition metal chalcogenides,[11,12,13,14] tremendous efforts have been made on obtaining QSH compounds with large bandgap, good stability, and ease of fabrication, which are all desirable properties for high-temperature low-dissipation device applications
In the past few years, most of the studies are focusing on the topological properties in bulk ZrTe5,16–25 which are rather controversial because they are predicted to be located near the boundary of the strong topological insulator (STI) phase and the weak topological insulator (WTI) phase, aLiu and Wang contributed to this work. bAuthors to whom correspondence should be addressed: liuzhk@shanghaitech.edu.cn and yulin.chen@physics.ox.ac.u.k, .s
Summary
Quantum Spin Hall (QSH) insulators are quantum materials with a bulk insulating gap and helical transport channels at the edge protected by time reversal symmetry (TRS) without backscattering,[1,2,3,4] making them good candidates for dissipationless transport. By the combination of ARPES and STM/STS experiments, we systematically investigated the electronic structure of bulk HfTe5 to address its topological nature.
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