Experimental realization of a topological crystalline insulator in SnTe

TL;DR

This paper provides the first experimental evidence of a topological crystalline insulator phase in SnTe, confirming theoretical predictions and revealing mirror-symmetry protected metallic surface states.

Contribution

It experimentally verifies the existence of a TCI phase in SnTe, demonstrating mirror-symmetry protected surface states via angle-resolved photoemission spectroscopy.

Findings

SnTe exhibits a Dirac-cone surface band with a Dirac point away from the zone edge.

PbTe lacks such gapless surface states, aligning with theoretical predictions.

The results confirm SnTe as a topological crystalline insulator.

Abstract

Topological insulators materialize a topological quantum state of matter where unusual gapless metallic state protected by time-reversal symmetry appears at the edge or surface. Their discovery stimulated the search for new topological states protected by other symmetries, and a recent theory predicted the existence of "topological crystalline insulators" (TCIs) in which the metallic surface states are protected by mirror symmetry of the crystal. However, its experimental verification has not yet been reported. Here we show the first and definitive experimental evidence for the TCI phase in tin telluride (SnTe) which was recently predicted to be a TCI. Our angle-resolved photoemission spectroscopy shows clear signature of a metallic Dirac-cone surface band with its Dirac point slightly away from the edge of the surface Brillouin zone in SnTe. On the other hand, such a gapless surface state is absent in a cousin material lead telluride (PbTe), in line with the theoretical prediction. Our result establishes the presence of a TCI phase, and opens new avenues for exotic topological phenomena.