Berlin 2018 – scientific programme

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 3: Crystal Structure, Defects, Real Structure and Microstructure in Materials

KFM 3.1: Talk

Monday, March 12, 2018, 09:30–09:50, E 124

Higher-Order Topological Insulators — •Frank Schindler¹, Ashley Cook¹, Maia Vergniory², Zhijun Wang³, Stuart Parkin⁴, Andrei Bernevig³, and Titus Neupert¹ — ¹University of Zurich, Switzerland — ²University of the Basque Country, Spain — ³Princeton University, USA — ⁴Max Planck Institute of Microstructure Physics, Germany

Three-dimensional topological (crystalline) insulators are materials with an insulating bulk, but conducting surface states which are topologically protected by time-reversal (or spatial) symmetries.

Here, we extend the notion of three-dimensional topological insulators to systems that host no gapless surface states, but exhibit topologically protected gapless hinge states. Their topological character is protected by spatio-temporal symmetries, of which we present two cases: (1) Chiral higher-order topological insulators protected by the combination of time-reversal and a four-fold rotation symmetry. Their hinge states are chiral modes and the bulk topology is Z2-classified. (2) Helical higher-order topological insulators protected by time-reversal and mirror symmetries. Their hinge states come in Kramers pairs and the bulk topology is Z-classified.

We provide the topological invariants for both cases. Furthermore, we discuss current developments concerning material realizations of these novel phases of matter.