Two-Dimensional Group-IV Chalcogenide Si2Te2 film: A New Quantum Spin Hall Insulator with Sizable Band Gap

TL;DR

This paper predicts a new 2D Si2Te2 film as a quantum spin Hall insulator with a sizable, tunable band gap, promising for topological spintronics, using first-principles calculations.

Contribution

It introduces Si2Te2 as a novel 2D QSH insulator with a sizable, strain-tunable band gap and demonstrates its potential for spintronics applications.

Findings

Si2Te2 is a 2D QSH insulator with a 0.29 eV band gap.

The topological phase is due to band inversion between Si-px,y and Te-px,y orbitals.

Edge states can be tuned by edge modifications and substrate choice.

Abstract

Quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices due to the robust gapless states inside insulating bulk gap. Here, by using first-principles calculations, we discover group-IV chalcogenide Si2Te2 film to be a 2D QSH insulator with a fundamental band gap of 0.29 eV, which is tunable under external strain. This nontrivial topological phase stems from band inversion between the Si-px,y and Te-px,y orbitals, demonstrated by a single pair of topologically protected helical edge states with Dirac point locating in the bulk gap. Notably, the characteristic properties of edge states, such as the Fermi velocity and edge shape, can be tuned by edge modifications. Additionally, the h-BN semiconductor is an ideal substrate for experimental realization of 2D Si2Te2 film, without destroying its nontrivial topology. Our works open a new route for designing topological spintronics devices based on 2D silicon-based films.