Suppression of metal-to-insulator transition and appearance of superconductivity in Cu1-xZnxIr2S4 - art. no. 214514

The thiospinel system Cu1-xZnxIr2S4 (0 less than or equal tox less than or equal to0.9) has been studied by x-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. The parent compound CuIr2S4, bei ng metallic at room temperature, undergoes a structural phase transition to wards lower symmetry around 230 K and becomes an insulator at the low tempe rature. The Zn substitution for Cu was found to drastically suppress the me tal-to-insulator (MI) transition, resulting in the appearance of supercondu ctivity. The MI transition temperature T-MI and the extent of the structura l distortion both decrease with increasing x until the phase transition is completely suppressed at x similar to0.4. In the region of x less than or e qual to0.4, the cubic spinel phase coexists with the low-symmetry phase bel ow T-MI. For the metallic phase, the change of the Pauli paramagnetic susce ptibility indicates the hole-filling mechanism due to an excess electron fr om the Zn substitution for Cu. The insulating state of the low-symmetry pha se is tentatively explained in terms of charge ordering combined with the I r4+ dimerization. Bulk type-II superconductivity below 3.4 K is observed fo r 0.25 less than or equal tox less than or equal to0.8 samples. The superco nducting transition temperature decreases with increasing the Zn content. T he abnormal behavior of the normal-state resistivity below 200 K for 0.3 le ss than or equal tox less than or equal to0.5 samples suggests modification of the electronic states, which might be related to the occurrence of supe rconductivity.