High-temperature helical edge states in BiSbTeSe2/graphene van der Waals heterostructure
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Van der Waals heterostructures have been used to tailor atomic layers into various artificial materials through interactions at heterointerfaces. The interplay between the band gap created by the band folding of the interfacial potential and the band inversion driven by enhanced spin-orbit interaction (SOI) through band hybridization enables us to realize a two-dimensional topological insulator (2D-TI). Here we report the realization of graphene 2D-TIs by epitaxial growth of three-dimensional topological insulator (3D-TI) BiSbTeSe 2 ultrathin films on graphene. Increasing the thickness of the BiSbTeSe 2 films from 2 nm to 9 nm enhances the SOI on graphene and alters the electronic state from a trivial Kekulé insulator to a 2D-TI. Nonlocal transport reveals the helical edge conduction that survives up to 200 K. Our graphene 2D-TI is stable and easy to make electrical contacts, and it is of high quality. It offers various applications including spin-current conversion and platforms for Majorana fermions in junctions with superconductors.
