2017/08/31 by Frank Schindler, Ashley M. Cook, Maia G. Vergniory +4 · 3 citations
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.mtrl-sci #cond-mat.str-el
paper · pdf · doi:10.1126/sciadv.aat0346
published as Science Advances 01 Jun 2018: Vol. 4, no. 6, eaat0346 · 8 pages (4 figures) and 16 pages supplemental material (7 figures)
arxiv created 2018/06/03 · arxiv updated 2018/06/05
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 show that SnTe as well as surface-modified Bi2TeI, BiSe, and BiTe are helical higher-order topological insulators and propose a realistic experimental setup to detect the hinge states.