Flat AgTe Honeycomb Monolayer with Topologically Nontrivial States

TL;DR

This study reports the synthesis and characterization of a stable, monolayer AgTe honeycomb structure exhibiting topologically nontrivial quantum spin Hall states, with potential applications in electronic devices.

Contribution

It is the first demonstration of a stable, free-standing AgTe monolayer with topologically nontrivial states protected by mirror symmetry.

Findings

AgTe monolayer has a honeycomb structure confirmed by microscopy and diffraction.

Spin-orbit coupling opens a gap leading to quantum spin Hall edge states.

The monolayer AgTe is chemically stable under ambient conditions.

Abstract

The intriguing properties, especially Dirac physics in graphene, have inspired the pursuit of two-dimensional materials in honeycomb structure. Here we achieved a monolayer transition metal monochalcogenide AgTe on Ag(111) by tellurization of the substrate. High-resolution scanning tunneling microscopy, combined with low-energy electron diffraction, angle-resolved photoemission spectroscopy, and density functional theory calculations, demonstrates the planar honeycomb structure of AgTe. The first principle calculations further reveal that, protected by the in-plane mirror reflection symmetry, two Dirac node-line Fermions exist in the electronic structures of free-standing AgTe when spin-orbit coupling (SOC) is ignored. While in fact the SOC leads to the gap opening, and resulting in the emergence of the topologically nontrivial quantum spin Hall edge state. Importantly, our experiments evidence the chemical stability of the monolayer AgTe in ambient conditions. It is possible to study AgTe by more ex-situ measurements and even to apply it in novel electronic devices.