Topological Crystalline Insulators in the SnTe Material Class

TL;DR

This paper predicts that SnTe is a topological crystalline insulator with metallic surface states protected by crystal symmetry, and discusses how symmetry breaking can tune its electronic properties for various applications.

Contribution

The first prediction of SnTe as a topological crystalline insulator based on its topological index and surface state analysis.

Findings

SnTe has metallic surface states with Dirac cones on high-symmetry surfaces.

Surface states are protected by reflection symmetry and are robust against disorder.

Breaking mirror symmetry can tune the surface band gap.

Abstract

Topological crystalline insulators are new states of matter in which the topological nature of electronic structures arises from crystal symmetries. Here we predict the first material realization of topological crystalline insulator in the semiconductor SnTe, by identifying its nonzero topological index. We predict that as a manifestation of this nontrivial topology, SnTe has metallic surface states with an even number of Dirac cones on high-symmetry crystal surfaces such as {001}, {110} and {111}. These surface states form a new type of high-mobility chiral electron gas, which is robust against disorder and topologically protected by reflection symmetry of the crystal with respect to {110} mirror plane. Breaking this mirror symmetry via elastic strain engineering or applying an in-plane magnetic field can open up a continuously tunable band gap on the surface, which may lead to wide-ranging applications in thermoelectrics, infrared detection, and tunable electronics. Closely related semiconductors PbTe and PbSe also become topological crystalline insulators after band inversion by pressure, strain and alloying.