Journal Article

Observation of topologically protected states at crystalline phase boundaries in single-layer WSe 2

Chen, Yi, Mo, Sung-Kwan, Zhang, Yi, Crommie, Michael F, Ugeda, Miguel M, Wang, Feng, Yazyev, Oleg V, Ryu, Hyejin, Shen, Zhi-Xun, Martín-Recio, Ana, Tang, Shujie, Wong, Dillon, Pulkin, Artem, Pedramrazi, Zahra, Wu, Quansheng

2018

Overview

Transition metal dichalcogenide materials are unique in the wide variety of structural and electronic phases they exhibit in the two-dimensional limit. Here we show how such polymorphic flexibility can be used to achieve topological states at highly ordered phase boundaries in a new quantum spin Hall insulator (QSHI), 1T'-WSe . We observe edge states at the crystallographically aligned interface between a quantum spin Hall insulating domain of 1T'-WSe and a semiconducting domain of 1H-WSe in contiguous single layers. The QSHI nature of single-layer 1T'-WSe is verified using angle-resolved photoemission spectroscopy to determine band inversion around a 120 meV energy gap, as well as scanning tunneling spectroscopy to directly image edge-state formation. Using this edge-state geometry we confirm the predicted penetration depth of one-dimensional interface states into the two-dimensional bulk of a QSHI for a well-specified crystallographic direction. These interfaces create opportunities for testing predictions of the microscopic behavior of topologically protected boundary states.