Superconductivity and its underlying mechanisms are one of the most active research fields in condensed-matter physics. An important question is how to enhance the transition temperature $T_{ \rm c}$ of a superconductor. In this respect, the possibly positive role of valence-skipping elements in the pairing mechanism has been attracting considerable interest. Here we follow this pathway and successfully enhance $T_{ \rm c}$ up to almost 6 K in the simple chalcogenide SnTe known as topological crystalline insulator by doping the valence-skipping element In and codoping Se. A high-pressure synthesis method enabled us to form single-phase solid solutions Sn$_{ 1-x}$In$_{ x}$Te$_{ 1-y}$Se$_{ y}$ over a wide composition range while keeping the cubic structure necessary for the superconductivity. Our experimental results are supported by density-functional theory calculations which suggest that even higher $T_{ \rm c}$ values would be possible if the required doping range were experimentally accessible.
Categories: cond-mat.supr-con