Topological edge states at single layer WSe2 1T′–1H lateral heterojunctions

Abstract

Transition metal dichalcogenides can be epitaxially grown at the single layer limit, which also adopt a variety of structural polymorphs with significantly different electronic properties. Lateral heterostructures of different polymorphs can be further synthesized for emergent functionality. Here, we selectively grow semiconducting 1H and metastable 1T′ phases of WSe2 on epitaxial graphene/SiC(0001) by molecular beam epitaxy and further show that the 1T′ phase is a two-dimensional topological insulator. Using angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, we determine that 1T′–WSe2 exhibits a large bulk bandgap of 120 meV, and edge states at the 1T′–1H lateral heterojunction extend within 1.6 nm from the heterointerface at the 1T′ side. These edge states are robust and persist regardless of the fact that if the edge is (1 × 1) zigzag or (3 × 1) reconstructed, confirming their topological nature. This further facilitates the epitaxial growth of 1T′–1H lateral junction superlattices with multiple helical edge channels, underpinning ultrahigh-density 2D topological nano quantum devices.