Topological quantum phase transition from mirror to time reversal symmetry protected topological insulator

Partha S Mandal,Valentine V Volobuev,Ondrej Caha,Jaime Sánchez-Barriga,Günther Bauer,Gunther Springholz,Evangelos Golias,Andrei Varykhalov,Oliver Rader

doi:10.1038/s41467-017-01204-0

Abstract

Topological insulators constitute a new phase of matter protected by symmetries. Time-reversal symmetry protects strong topological insulators of the Z2 class, which possess an odd number of metallic surface states with dispersion of a Dirac cone. Topological crystalline insulators are merely protected by individual crystal symmetries and exist for an even number of Dirac cones. Here, we demonstrate that Bi-doping of Pb1−xSnxSe (111) epilayers induces a quantum phase transition from a topological crystalline insulator to a Z2 topological insulator. This occurs because Bi-doping lifts the fourfold valley degeneracy and induces a gap at bar Gamma , while the three Dirac cones at the {bar{rm M}} points of the surface Brillouin zone remain intact. We interpret this new phase transition as caused by a lattice distortion. Our findings extend the topological phase diagram enormously and make strong topological insulators switchable by distortions or electric fields.

Highlights

Topological insulators constitute a new phase of matter protected by symmetries
We show that when Bi is introduced in the bulk making the system n-type, a gap is opened up at the one Dirac cone at the center of the surface Brillouin zone at Γ, while the three Dirac cones located at the M points at the zone boundaries behave as in pure Pb1−xSnxSe, that is, are gapless at low temperature
Our findings provide the first experimental evidence for a topological phase transition from a topological crystalline insulators (TCIs) with an even number of Dirac cones to a Z2 time-reversal symmetry-protected strong topological insulator where the

Summary

Introduction

Topological insulators constitute a new phase of matter protected by symmetries. Timereversal symmetry protects strong topological insulators of the Z2 class, which possess an odd number of metallic surface states with dispersion of a Dirac cone. We demonstrate that Bi-doping of Pb1−xSnxSe (111) epilayers induces a quantum phase transition from a topological crystalline insulator to a Z2 topological insulator This occurs because Bi-doping lifts the fourfold valley degeneracy and induces a gap at Γ, while the three Dirac cones at the M points of the surface Brillouin zone remain intact. The lattice contracts and the enhanced orbital overlap leads to an inverted (i.e., negative) bulk band gap, which, via bulk-boundary correspondence, gives rise to Dirac cone surface states. This has impressively been shown by temperaturedependent angle-resolved photoemission (ARPES)[15].

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Results

Conclusion