Strain-induced two-dimensional topological crystalline insulator

TL;DR

This paper reports the experimental realization of a two-dimensional topological crystalline insulator in bilayer SnTe, demonstrating edge states with potential applications in spintronics and nanoelectronics at room temperature.

Contribution

It presents the growth, characterization, and theoretical identification of a 2D TCI in bilayer SnTe, overcoming previous material challenges.

Findings

Observation of two pairs of edge states with a large band gap

Experimental evidence of 2D TCI states in bilayer SnTe

Demonstration of tunable topological edge state coupling

Abstract

Topological crystalline insulators (TCIs) host topological phases of matter protected by crystal symmetries. Topological surface states in three-dimensional TCIs have been predicted and observed in IV-VI SnTe-class semiconductors. Despite the prediction of a two-dimensional (2D) TCI characterized by two pairs of edge states inside the bulk gap, materials challenges have thus far prevented its experimental realization. Here we report the growth and characterization of bilayer SnTe on the 2$H$-NbSe$_2$ substrate by molecular beam epitaxy and scanning tunneling microscopy. We experimentally observe two anticorrelated, periodically modulated pairs of conducting edge states along the perimeters of the sample with a large band gap exceeding $0.2$ eV. We identify these states with a 2D TCI through first principles calculations. Finally, we probe the coupling of adjacent topological edge states and demonstrate the resulting energy shift driven by a combination of electrostatic interactions and tunneling coupling. Our work opens the door to investigations of tunable topological states in 2D TCIs, of potential impact for spintronics and nanoelectronics applications at room temperature.