Experimental Realization of the Topologically Nontrivial Phase in Monolayer Si$_2$Te$_2$

TL;DR

This study experimentally demonstrates the growth of monolayer Si$_2$Te$_2$ on HfTe$_2$, confirming its topological quantum spin Hall phase through microscopy, spectroscopy, and theoretical calculations, marking a significant step toward room-temperature topological devices.

Contribution

It provides the first experimental realization of monolayer Si$_2$Te$_2$ with preserved topological properties using HfTe$_2$ as a substrate.

Findings

Confirmation of strain-free monolayer Si$_2$Te$_2$ with a sizable band gap

Observation of topologically protected edge states at step edges

First-principles calculations support experimental topological phase

Abstract

The free-standing monolayer Si$_2$Te$_2$ (ML-Si$_2$Te$_2$) has been theoretically predicted to host a room-temperature quantum spin Hall phase. However, its experimental realization remains challenge due to the absence of a three-dimensional counterpart. Here, we demonstrate that HfTe$_2$ serves as an ideal substrate for the epitaxial growth of ML-Si$_2$Te$_2$, preserving its topological phase. Scanning tunneling microscopy and spectroscopy confirm a strain-free ${(1 \times 1)}$ lattice of ML-Si$_2$Te$_2$, along with a sizable band gap, which is well captured by first-principles calculations. Moreover, distinct edge states, independent of step geometry and exhibiting a broad spatial distribution, are observed at ML-Si$_2$Te$_2$ step edges, underscoring its topological nature.