Superconductivity in La2O2M4S6 -Type Bi-based Compounds: A Review on Element Substitution Effects

Abstract

Since 2012, layered compounds containing Bi-Ch (Ch: S and Se) layers have been extensively studied in the field of superconductivity. The most-studied system is BiS2-based superconductors with two-layer-type conducting layers. Recently, superconductivity was observed in La2O2M2S6 (M = metals), which contains four-layer-type conducting layers. The four-layer-type Bi-based superconductors are new systems in the family of Bi-based superconductors; we can expect further development of Bi-based layered superconductors. In this review article, we summarize the progress of synthesis, structural analysis, investigations on superconducting properties, and material design of the four-layer-type Bi-based superconductors. In-plane chemical pressure is the factor essential for the emergence of bulk superconductivity in the system. The highest Tc of 4.1 K was observed in Rare Earth elements (RE) substituted La2-xRExO2Bi3Ag0.6Sn0.4S6.