Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors

Abstract

Recent theoretical studies employing density-functional theory have predicted BaBiO 3 (when doped with electrons) and YBiO 3 to become a topological insulator (TI) with a large topological gap (∼0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba 1-x K x BiO 3 and BaPb 1-x Bi x O 3, which are "high-Tc" bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy E F a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above E F. Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below E F for further hole doping, which manifests these systems to be candidates for both electron- and hole-doped topological insulators.