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

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. The superconductivity was induced by separating 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 the unit cell tetragonality (c/a), implying a key role of relative separation of the Bi square nets to induce the superconductivity.