title: Topologically protected surface states in a centrosymmetric superconductor β-PdBi2.
abstract: The topological aspects of electrons in solids can emerge in real materials, as represented by topological insulators. In theory, they show a variety of new magneto-electric phenomena, and especially the ones hosting superconductivity are strongly desired as candidates for topological superconductors. While efforts have been made to develop possible topological superconductors by introducing carriers into topological insulators, those exhibiting indisputable superconductivity free from inhomogeneity are very few. Here we report on the observation of topologically protected surface states in a centrosymmetric layered superconductor, β-PdBi2, by utilizing spin- and angle-resolved photoemission spectroscopy. Besides the bulk bands, several surface bands are clearly observed with symmetrically allowed in-plane spin polarizations, some of which crossing the Fermi level. These surface states are precisely evaluated to be topological, based on the Z2 invariant analysis in analogy to three-dimensional strong topological insulators. β-PdBi2 may offer a solid stage to investigate the topological aspect in the superconducting condensate.
authors.affiliation: Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Sakano
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology, Kanagawa 226-8503, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Okawa
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology, Kanagawa 226-8503, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kanou
authors.affiliation: Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sanjo
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Okuda
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology, Kanagawa 226-8503, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sasagawa
authors.affiliation: Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ishizaka