SnO

Antiperovskite (inverse perovskite) oxides are the materials crystallizing in the same structure as the ordinary perovskite oxides but with the inverted positions of the metal element and oxygen. Some of these materials are theoretically suggested to be topological crystalline insulators based on the first-principles calculations [1, 2].
We discovered the first superconductivity among this group of oxides in Sr_3−xSnO [3]. Reflecting the topology of the electronic band structure in the normal state, a topological superconductivity is theoretically proposed in this compound [3, 4]. In order to investigate the nature of the superconducting state, we performed the muon spin rotation (μSR) experiment. Under small magnetic fields, we successfully observed increase of the relaxation rate of μ⁺ below the transition temperature and confirmed the bulk superconductivity. The ratio between the relaxation rate and transition temperature σ/T_c is much smaller than those of the conventional superconductors and close to the values known for unconventional ones.

[1] T. Kariyado and M. Ogata, J. Phys. Soc. Jpn. 80, 083704 (2011).
[2] T. H. Hsieh et al., Phys. Rev. B 90, 081112(R) (2014).
[3] M. Oudah, A. Ikeda et al., Nat. Commun. 7, 13617 (2016).
[4] T. Kawakami et al., Phys. Rev. X 8, 041026 (2018).