Topologically protected surface states in a centrosymmetric superconductor β-PdBi2

• Published in: Nature communications 2015-10, Vol.6 (1), p.8595-8595, Article 8595
• Main Authors: Sakano, M., Okawa, K., Kanou, M., Sanjo, H., Okuda, T., Sasagawa, T., Ishizaka, K
• Format: Article
• Language: English
• Subjects: 140/146; 639/766/119/1003; 639/766/119/2792; 639/766/25; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms9595

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-PdBi 2 , 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 Z 2 invariant analysis in analogy to three-dimensional strong topological insulators. β-PdBi 2 may offer a solid stage to investigate the topological aspect in the superconducting condensate. Materials possessing topologically non-trivial electronic surface states are predicted to host exotic Majorana fermion excitations in the superconducting state. Here, the authors demonstrate the existence of topologically-protected surface states in the centrosymmetric layered superconductor β-PdBi2.