Discovery of BiS2-Based Superconductor and Material Design Concept

In 2012, we discovered new layered superconductors whose superconducting states emerge in the BiS2 layers. Since their crystal structure, composed of alternate stacks of BiS2 conduction layers and electrically insulating (blocking) layers, is similar to those of cuprate and Fe-based superconductors, many researchers have explored new BiS2-based superconductors and have studied the physical and chemical properties of the BiS2-based superconductors. In this paper, we present the histories of the discovery of the first BiS2-based superconductor, Bi4O4S3, and the second one, LaO1−xFxBiS2. The structural variation of the BiS2-based superconductor family is briefly introduced. Then, we show the material design concept for the emergence of bulk superconductivity in BiS2-based compounds. At the end, a possible strategy for the enhancement of the transition temperature in the BiS2-based superconductors is proposed.