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

TL;DR

This paper predicts that hole- and electron-doped Bismuth-Oxide superconductors may also exhibit topological insulating states with Dirac surface states, revealing a potential coexistence of superconductivity and topological order.

Contribution

It introduces the prediction of topological insulating phases in doped Bismuth-Oxide superconductors, highlighting their dual potential for superconductivity and topological properties.

Findings

K-doped Bismuth-Oxides are topological insulators with a large gap.

Presence of Dirac cones both above and below the Fermi level with doping.

Potential coexistence of superconductivity and topological surface states.

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.