Suppression of metal-to-insulator transition and appearance of superconductivity in Cu1−xZnxIr2S4

Abstract

The thiospinel system Cu1−xZnxIr2S4 (0<~x<~0.9) has been studied by x-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. The parent compound CuIr2S4, being metallic at room temperature, undergoes a structural phase transition towards lower symmetry around 230 K and becomes an insulator at the low temperature. The Zn substitution for Cu was found to drastically suppress the metal-to-insulator (MI) transition, resulting in the appearance of superconductivity. The MI transition temperature TMI and the extent of the structural distortion both decrease with increasing x until the phase transition is completely suppressed at x∼0.4. In the region of x<~0.4, the cubic spinel phase coexists with the low-symmetry phase below TMI. For the metallic phase, the change of the Pauli paramagnetic susceptibility indicates the hole-filling mechanism due to an excess electron from the Zn substitution for Cu. The insulating state of the low-symmetry phase is tentatively explained in terms of charge ordering combined with the Ir4+ dimerization. Bulk type-II superconductivity below 3.4 K is observed for 0.25<~x<~0.8 samples. The superconducting transition temperature decreases with increasing the Zn content. The abnormal behavior of the normal-state resistivity below 200 K for 0.3<~x<~0.5 samples suggests modification of the electronic states, which might be related to the occurrence of superconductivity.

Source-reported materials — not catalogue approval

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