Evolution of Superconductivity with Sr-Deficiency in Antiperovskite Oxide SrSnO.

Bulk superconductivity was recently reported in the antiperovskite oxide SrSnO, with a possibility of hosting topological superconductivity. We investigated the evolution of superconducting properties such as the transition temperature T and the size of the diamagnetic signal, as well as normal-state electronic and crystalline properties, with varying the nominal Sr deficiency x. Polycrystalline SrSnO was obtained up to x = 0:6 with a small amount of SrO impurities. The amount of impurities increases for x > 0.6, suggesting phase instability for high deficiency. Mössbauer spectroscopy reveals an unusual Sn ionic state in both stoichiometric and deficient samples. By objectively analyzing superconducting diamagnetism data obtained from a large number of samples, we conclude that the optimal x lies in the range 0.5 < x < 0.6. In all superconducting samples, two superconducting phases appear concurrently that originate from SrSnO but with varying intensities. These results clarify the Sr deficiency dependence of the normal and superconducting properties of the antiperovskite oxide SrSnO will ignite future work on this class of materials.