Large gap two dimensional topological insulators: bilayer triangular lattice TlM (M = N, P, As, Sb)

TL;DR

This paper predicts that bilayer TlM (M = N, P, As, Sb) materials can exhibit quantum spin Hall effect due to p-p band inversion, with large band gaps suitable for room temperature applications.

Contribution

It introduces a new class of 2D topological insulators based on bilayer triangular lattice TlM with p-p band inversion independent of spin-orbit coupling.

Findings

Quantum spin Hall effect predicted in bilayer TlM materials.

Maximal band gap reaches 550 meV in TlSb.

Potential for room temperature topological electronic devices.

Abstract

Based on density functional theory and Berry curvature calculations, we predict that p-p band inversion type quantum spin Hall effect (QSHE) can be realized in a series of two dimensional (2D) bilayer honeycomb TlM (M = N, P, As, Sb), which can be effectively equivalent to bilayer triangular lattice for low energy electrons. Further topological analysis reveals that the band inversion between pz- and px,y of M atom contributes to the nontrivial topological nature of TlM. The band inversion is independent of spin-orbit coupling which is distinctive from conventional topological insulators (TIs). A tight binding model based on triangle lattice is constructed to describe the QSH states in the systems. Besides the interesting 2D triangular lattice $p-p$ type inversion for the topological mechanism, the maximal local band gap of the systems can reach 550 meV (TlSb), which provides a new choice for future room temperature quantum spin Hall Insulator (QSHI). Considering the advance of the technology of van der Waals passivation, combining with hexagonal materials, such as h-BN, TlMs show great potential for future 2D topological electronic devices.