Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum spin Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe2 single layer with the 1T' structure that does not exist in the bulk form of WSe2. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observed a gap of 129 meV in the 1T' layer and an in-gap edge state located near the layer boundary. The system's 2D TI characters are confirmed by first-principles calculations. The observed gap diminishes with doping by Rb adsorption, ultimately leading to an insulator-semimetal transition. The discovery of this large-gap 2D TI with a tunable band gap opens up opportunities for developing advanced nanoscale systems and quantum devices.
@article{arxiv.1805.08276,
title = {Quantum-spin-Hall insulator with a large gap: single-layer 1T' WSe$_2$},
author = {P. Chen and W. -W. Pai and Y. -H. Chan and W. -L. Sun and C. -Z. Xu and D. -S. Lin and M. Y. Chou and A. -V. Fedorov and T. -C. Chiang},
journal= {arXiv preprint arXiv:1805.08276},
year = {2018}
}