High-buckled R3 stanene with topologically nontrivial energy gap

TL;DR

This paper demonstrates a method to induce a topologically nontrivial energy gap in stanene by tuning atomic buckling, resulting in a high-buckled R3 stanene with confirmed topological edge states.

Contribution

It introduces a growth technique to produce high-buckled R3 stanene with a nontrivial energy gap, advancing control over 2D topological insulators.

Findings

High-buckled R3 stanene exhibits a large topological energy gap.

Edge states confirm the nontrivial topology of R3 stanene.

Tuning buckling enhances the quantum spin Hall effect in stanene.

Abstract

Stanene has been predicted to be a two-dimensional topological insulator (2DTI). Its low-buckled atomic geometry and the enhanced spin-orbit coupling are expected to cause a prominent quantum spin hall (QSH) effect. However, most of the experimentally grown stanene to date displays a metallic state without a real gap, possibly due to the chemical coupling with the substrate and the stress applied by the substrate. Here,we demonstrate an efficient way of tuning the atomic buckling in stanene to open a topologically nontrivial energy gap. Via tuning the growth kinetics, we obtain not only the low-buckled 1x1 stanene but also an unexpected high-buckled R3xR3 stanene on the Bi(111) substrate. Scanning tunneling microscopy (STM) study combined with density functional theory (DFT) calculation confirms that the R3xR3 stanene is a distorted 1x1 structure with a high-buckled Sn in every three 1x1 unit cells. The high-buckled R3xR3 stanene favors a large band inversion at the {\Gamma} point, and the spin orbital coupling open a topologically nontrivial energy gap. The existence of edge states as verified in both STM measurement and DFT calculation further confirms the topology of the R3xR3 stanene. This study provides an alternate way to tune the topology of monolayer 2DTI materials.