title: Topological crystalline insulator states in Pb(1-x)Sn(x)Se.
abstract: Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection. In this study we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a TCI for x  =  0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.
authors.affiliation: Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Dziawa
authors.forename: B J
authors.initials: BJ
authors.lastname: Kowalski
authors.forename: K
authors.initials: K
authors.lastname: Dybko
authors.forename: R
authors.initials: R
authors.lastname: Buczko
authors.forename: A
authors.initials: A
authors.lastname: Szczerbakow
authors.forename: M
authors.initials: M
authors.lastname: Szot
authors.forename: E
authors.initials: E
authors.lastname: Łusakowska
authors.forename: T
authors.initials: T
authors.lastname: Balasubramanian
authors.forename: B M
authors.initials: BM
authors.lastname: Wojek
authors.forename: M H
authors.initials: MH
authors.lastname: Berntsen
authors.forename: O
authors.initials: O
authors.lastname: Tjernberg
authors.forename: T
authors.initials: T
authors.lastname: Story