Metal-Insulator Transition and Superconductivity in Spinel-Type System Cu_{<b>1</b>-<i><i>x</i></i>}Zn_{<i><i>x</i></i>}Ir_<b>2</b>S_<b>4</b>

Abstract

The thiospinel compound CuIr 2 S 4 exhibits the metal-insulator (M-I) transition accompanied by the structural transition. In this work, compounds of Cu 1- x Zn x Ir 2 S 4 in the composition range 0≤ x ≤0.5 were synthesized to examine the effects of excess electrons supplied by replacing Cu with Zn. The samples were investigated by measurements of X-ray diffraction, electrical resistance and magnetic susceptibility. The M-I transition temperature T MI decreases with increasing x . Results are discussed on the basis of the model of charge ordering for the insulating state. It was found that the samples with x ≥0.3 show no M-I transition and exhibit superconductivity. The transition temperature T C is 2.8 K for x = 0.3 and 2.2 K for x = 0.5. The ground state of the system changes from insulating to superconducting with increasing Zn content.