Effects of Zn Doping on Superconductivity in Tl0.4K0.4Fe2-δ-x Zn x Se2

We have studied the transport and magnetic properties of the Tl0.4K0.4Fe2-delta-x Zn (x) Se-2 (nominal ratio 0.01a parts per thousand currency signxa parts per thousand currency sign0.15) single crystal samples. It is found that although Zn doping leads to a decrease of charge carrier density, it does not affect the superconductivity significantly when xa parts per thousand currency sign0.1. The doped superconductors exhibit properties similar to the parent compound (Tl0.4K0.4Fe2-delta Se-2), e.g., the almost unchanged superconducting transition temperature (T (c)) and the "hump"-like behavior in the resistivity curves, which denotes the transition from insulating phase to metallic phase. As the doping density rises, the hump obviously shifts to low temperature region, implying the quick enlargement of the ratio of insulating phase. The most plausible explanation for the above phenomena is that the Zn impurities prefer entering into the insulating phase only, therefore, merely hindering the formation of superconducting phase without directly changing its properties. The ESR measurement gives low signal-to-noise ratio and just weak paramagnetic signals, revealing strong itinerancy of the Zn doped superconductor.