Metal-Insulator Transition and Superconductivity in Spinel-Type System Cu_1-xZn_xIr₂S₄

抄録

The thiospinel compound CuIr₂S₄ exhibits the metal-insulator (M-I) transition accompanied by the structural transition. In this work, compounds of Cu_1-xZn_xIr₂S₄ 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≥q 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.