Two-Dimensional Superconductivity Emerged at Monatomic Bi^2- Square Net in Layered Y₂O₂Bi via Oxygen Incorporation

Discovery of layered superconductors such as cuprates and iron-based compounds has unveiled new science and compounds. In these superconductors, quasi-two-dimensional layers including transition metal cations play principal role in the superconductivity via carrier doping by means of aliovalent-ion substitution. Here, we report on a two-dimensional superconductivity at 2 K in ThCr₂Si₂-type layered oxide Y₂O₂Bi possessing conducting monatomic Bi^2- square net, possibly associated with an exotic superconductivity. The superconductivity emerges only in excessively oxygen-incorporated Y₂O₂Bi with expanded inter-net distance, in stark contrast to nonsuperconducting pristine Y₂O₂Bi reported previously. This result suggests that the element incorporation into hidden interstitial site could be an alternative approach to conventional substitution and intercalation methods for search of novel superconductors.