Superconductivity in electron-doped layer-structured nitride halides

New types of quasi two-dimensional superconductors have been developed. They consist of metal nitride layers sandwiched by halogen layers. On electron doping by the intercalation of alkali metals between the halide layers, the compounds changed into metals and showed superconductivity at relatively high transition temperatures up to 25.5 K. The newly developed superconductors show novel characteristics which cannot be interpreted by a conventional BCS concept.