Tailoring band structure and band filling in a simple cubic (IV, III)-VI superconductor

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_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_c up to almost 6 K in the simple chalcogenide SnTe known as a topological crystalline insulator by doping the valence-skipping element In substitutionally for the Sn site and codoping Se for the Te site. A high-pressure synthesis method enabled us to form single-phase solid solutions Sn_{1 -x}In_xTe_{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_c values would be possible if the required doping range was experimentally accessible.