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|Abstract:||The mathematical field of topology has become a framework in which to describe the low-energy electronic structure of crystalline solids. Typical of a bulk insulating three-dimensional topological crystal are conducting two-dimensional surface states. This constitutes the topological bulk-boundary correspondence. Here, we establish that the electronic structure of bismuth, an element consistently described as bulk topologically trivial, is in fact topological and follows a generalized bulk-boundary correspondence of higher-order: not the surfaces of the crystal, but its hinges host topologically protected conducting modes. These hinge modes are protected against localization by time-reversal symmetry locally, and globally by the three-fold rotational symmetry and inversion symmetry of the bismuth crystal. We support our claim theoretically and experimentally. Our theoretical analysis is based on symmetry arguments, topological indices, first-principles calculations, and the recently introduced framework of topological quantum chemistry. We provide supporting evidence from two complementary experimental techniques. With scanning-tunnelling spectroscopy, we probe the signatures of the rotational symmetry of the one-dimensional states located at the step edges of the crystal surface. With Josephson interferometry, we demonstrate their universal topological contribution to the electronic transport. Our work establishes bismuth as a higher-order topological insulator.|
|Electronic Publication Date:||30-Jul-2018|
|Citation:||Schindler, Frank, Wang, Zhijun, Vergniory, Maia G, Cook, Ashley M, Murani, Anil, Sengupta, Shamashis, Kasumov, Alik Yu, Deblock, Richard, Jeon, Sangjun, Drozdov, Ilya, Bouchiat, Helene, Gueron, Sophie, Yazdani, Ali, Bernevig, B Andrei, Neupert, Titus. (2018). Higher-order topology in bismuth. NATURE PHYSICS, 14 (918+ - 918+). doi:10.1038/s41567-018-0224-7|
|Type of Material:||Journal Article|
|Journal/Proceeding Title:||NATURE PHYSICS|
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