Superconductivity in defective pyrite-type iridium chalcogenides IrxCh2 (Ch = Se and Te)

We report superconductivity in defective pyrite-type iridium chalcogenides IrxCh2. Maximum values of Tc of 6.4 K for Ir0.91Se2 and 4.7 K for Ir0.93Te2 were observed. It was found that Ir0.75Ch2 is close to the boundary between metallic and insulating states and IrxCh2 systems undergo nonmetal to metal transitions as x increases. On the basis of density functional theory calculations and the observed large variation in the Ch-Ch distance with x, we suggest that Ir0.75Ch2 is the parent compound for the present superconductors.