High-temperature helical edge states in BiSbTeSe$_2$/graphene van der Waals heterostructure

TL;DR

This paper demonstrates the creation of high-temperature two-dimensional topological insulator states in a graphene-based heterostructure with BiSbTeSe$_2$, showing robust helical edge conduction up to 200 K with potential for spintronics and quantum computing.

Contribution

It reports the epitaxial growth of BiSbTeSe$_2$ on graphene to realize 2D-TIs with high-temperature helical edge states, a novel approach in topological insulator research.

Findings

Helical edge conduction persists up to 200 K.

Transition from trivial insulator to 2D-TI with increasing BiSbTeSe$_2$ thickness.

High-quality, stable graphene-based 2D-TI platform.

Abstract

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. By increasing the BiSbTeSe$_2$ thickness from 2 nm to 9 nm to enhance SOI on graphene, the electronic state is altered from the trivial Kekul${\'e}$ insulator to the 2D-TI. The nonlocal transport reveals the helical edge conduction which survives up to 200 K at maximum. Our graphene 2D-TI is stable, easy to make electrical contacts, and of high quality. It offers various applications including spin-current conversion and platforms for Majorana fermions in junctions to superconductors.