Topology on a new facet of bismuth.

Author(s) Hsu, C.H.; Zhou, X.; Chang, T.R.; Ma, Q.; Gedik, N.; Bansil, A.; Xu, S.Y.; Lin, H.; Fu, L.
Journal Proc Natl Acad Sci U S A
Date Published 2019 Jun 13

Bismuth-based materials have been instrumental in the development of topological physics, even though bulk bismuth itself has been long thought to be topologically trivial. A recent study has, however, shown that bismuth is in fact a higher-order topological insulator featuring one-dimensional (1D) topological hinge states protected by threefold rotational and inversion symmetries. In this paper, we uncover another hidden facet of the band topology of bismuth by showing that bismuth is also a first-order topological crystalline insulator protected by a twofold rotational symmetry. As a result, its surface exhibits a pair of gapless Dirac surface states. Remarkably, these surface Dirac cones are "unpinned" in the sense that they are not restricted to locate at specific k points in the surface Brillouin zone. These unpinned 2D Dirac surface states could be probed directly via various spectroscopic techniques. Our analysis also reveals the presence of a distinct, previously uncharacterized set of 1D topological hinge states protected by the twofold rotational symmetry. Our study thus provides a comprehensive understanding of the topological band structure of bismuth.

DOI 10.1073/pnas.1900527116
ISSN 1091-6490
Citation Hsu C-, Zhou X, Chang T-, Ma Q, Gedik N, Bansil A, et al. Topology on a new facet of bismuth. Proc Natl Acad Sci USA. 2019.