Tetragonality induced superconductivity in anti-ThCr₂Si₂-type RE₂O₂Bi (RE = rare earth) with Bi square nets

We report a series of layered superconductors, anti-ThCr₂Si₂-type RE₂O₂Bi (RE = rare earth), composed of electrically conductive Bi square nets and magnetic insulating RE₂O₂ layers. Superconductivity was induced by separating the Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in RE₂O₂ layers. Intriguingly, the transition temperature of all RE₂O₂Bi including nonmagnetic Y₂O₂Bi was approximately scaled by unit cell tetragonality (c/a), implying a key role in the relative separation of the Bi square nets to induce superconductivity.