Superconductivity in the doped antiperovskite oxide Sr$_{3-x}$SnO

In the antiperovskite oxide $A_3B$O, oxygen atoms occupy the center of the ordinary perovskite structure and the $A$ metal octahedrally coordinate the oxygen. More interestingly, the $B$ metal exhibits a negative valence state, which is unusual for metallic ions. Because of such structural and electrical uniqueness, the antiperovskite oxides attracts much attention these days. In particular, the prediction of Dirac semimetal states in Ca$_3$PbO and its related compounds triggered extensive investigation [1]. Here, we report discovery of superconductivity in Sr$_{3-x}$SnO, based on the observation of zero resistivity and Meissner screening [2]. To the best of our knowledge, this compound is the first superconductor among the known antiperovskite oxides. In addition, this compound may host topological superconductivity, because of the strong orbital mixing of the underlying electronic state.\newline [1] T. Kariyado and M. Ogata, J. Phys. Soc. Jpn. \textbf{80}, 083704 (2011).\newline [2] M. Oudah \textit{et al.}, Nature Comm. \textbf{7}, 13617 (2016).