Quantum spin Hall (QSH) insulators exhibit spin-polarized conducting edge states that are topologically protected from backscattering and offer unique opportunities for addressing fundamental science questions and device applications. Finding viable materials that host such topological states, however, remains a challenge. Here by using in-depth first-principles theoretical modeling, we predict large bandgap QSH insulators in recently bottom-up synthesized two-dimensional (2D) MSi2Z4 (M = Mo or W and Z = P or As) materials family with 1T′ structure. A structural distortion in the 2H phase drives a band inversion between the metal (Mo/W) d and p states of P/As to realize spinless Dirac cone states without spin-orbit coupling. When spin-orbit coupling is included, a hybridization gap as large as ∼204 meV opens up at the band crossing points, realizing spin-polarized conducting edge states with nearly quantized spin Hall conductivity. We also show that the inverted band gap is tunable with a vertical electric field which drives a topological phase transition from the QSH to a trivial insulator with Rashba-like edge states. Our study identifies 2D MSi2Z4 materials family with 1T′ structure as large bandgap, tunable QSH insulators with protected spin-polarized edge states and large spin-Hall conductivity.
@article{arxiv.2207.08407,
title = {Switchable large-gap quantum spin Hall state in two-dimensional MSi$_2$Z$_4$ materials class},
author = {Rajibul Islam and Rahul Verma and Barun Ghosh and Zahir Muhammad and Arun Bansil and Carmine Autieri and Bahadur Singh},
journal= {arXiv preprint arXiv:2207.08407},
year = {2026}
}