Observation of Topologically Protected States at Crystalline Phase Boundaries in Single-layer WSe2
Miguel M. Ugeda,Miguel M. Ugeda,Miguel M. Ugeda,Artem Pulkin,Shujie Tang,Shujie Tang,Hyejin Ryu,Hyejin Ryu,QuanSheng Wu,Yi Zhang,Yi Zhang,Yi Zhang,Dillon Wong,Zahra Pedramrazi,Ana Martín-Recio,Ana Martín-Recio,Yi Chen,Feng Wang,Feng Wang,Zhi-Xun Shen,Zhi-Xun Shen,Sung-Kwan Mo,Oleg V. Yazyev,Michael F. Crommie,Michael F. Crommie +24 more
TL;DR: It is shown how polymorphic flexibility can be used to achieve topological states at highly ordered phase boundaries in a new quantum spin Hall insulator (QSHI), 1T′-WSe2, and the predicted penetration depth of one-dimensional interface states into the two-dimensional bulk of a QSHI for a well-specified crystallographic direction.
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Abstract: Transition metal dichalcogenide (TMD) materials are unique in the wide variety of structural and electronic phases they exhibit in the two-dimensional (2D) single-layer 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'-WSe2. We observe helical states at the crystallographically-aligned interface between quantum a spin Hall insulating domain of 1T'-WSe2 and a semiconducting domain of 1H-WSe2 in contiguous single layers grown using molecular beam epitaxy (MBE). The QSHI nature of single-layer 1T'-WSe2 was verified using ARPES to determine band inversion around a 120 meV energy gap, as well as STM spectroscopy to directly image helical edge-state formation. Using this new edge-state geometry we are able to directly confirm the predicted penetration depth of a helical interface state into the 2D bulk of a QSHI for a well-specified crystallographic direction. The clean, well-ordered topological/trivial interfaces observed here create new opportunities for testing predictions of the microscopic behavior of topologically protected boundary states without the complication of structural disorder.
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