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) BiSbTeSe2 ultrathin films on graphene. By increasing the BiSbTeSe2 thickness from 2 nm to 9 nm to enhance SOI on graphene, the electronic state is altered from the trivial Kekuleˊ 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.
@article{arxiv.2506.20510,
title = {High-temperature helical edge states in BiSbTeSe$_2$/graphene van der Waals heterostructure},
author = {Yoichi Tanabe and Ngoc Han Tu and Ming-Chun Jiang and Yi Ling Chiew and Mitsutaka Haruta and Kiyohiro Adachi and David Pomaranski and Ryo Ito and Yuya Shimazaki and Daisuke Hashizume and Xiuzhen Yu and Guang-Yu Guo and Ryotaro Arita and Michihisa Yamamoto},
journal= {arXiv preprint arXiv:2506.20510},
year = {2025}
}