Robust Large Gap Quantum Spin Hall Insulators in Methyl-functionalized III-Bi Buckled Honeycombs

TL;DR

This paper predicts methyl-functionalized III-Bi monolayers as large-gap quantum spin Hall insulators suitable for room-temperature spintronics, confirmed by first-principles calculations showing robust topological states and large band gaps.

Contribution

It introduces methyl-functionalized III-Bi monolayers as large-gap QSH insulators with robust topological properties confirmed by first-principles calculations.

Findings

Band gaps up to 0.843 eV suitable for room temperature.

Topological states confirmed by s-px,y band inversion and Z2 invariant.

Robustness against strain and methyl coverage variations.

Abstract

A large bulk band gap is critical for the applications of quantum spin hall (QSH) insulators in spintronics at room temperature. Based on first-principles calculations, we predict that the methyl-functionalized III-Bi monolayers, namely III-Bi-(CH3)2 (III=Ga, In, Tl) thin films, own QSH states with band gap as large as 0.260, 0.304 and 0.843 eV, respectively, making them suitable for room-temperature applications. The topological characteristics are confirmed by s-px,y band inversion, topological invariant Z2, and the topologically protected edge states. Noticeably, for GaBi/InBi-(CH3)2 films, the s-px,y band inversion occurred in the progress of spin-orbital coupling (SOC), while for TlBi(CH3)2 film, the s-px,y band inversion happened in the progress of chemical bonding. Significantly, the QSH states in III-Bi-(CH3)2 films are robust against the mechanical strains and various methyl coverages, making these films particularly flexible to substrate choice for device applications. Besides, the h-BN substrate is an ideal substrate for III-Bi-(CH3)2 films to realize large gap nontrivial topological states.. These findings demonstrate that the methyl-functionalized III-Bi films may be good QSH effect platforms for topological electronic devices design and fabrication in spintronics.