Effect of Zn impurity in K0.8Fe2−δ−xZnxSe2

A series of K0.8Fe2???xZnxSe2 single-crystal samples with nominal compositions 0???x???0.05 were grown and their physical properties were measured in order to study the effect of Zn impurity. It is found that the Zn impurity (x???0.02) does not affect the superconducting transition temperature Tc significantly. Meanwhile the hump in resistivity which corresponds to the transition from the insulating to metallic phase quickly shifts towards low temperatures. The results imply that there should be a phase separation in this system and Zn impurity causes the enhancement of the insulating phase. The negligible effect of Zn impurity on Tc suggests an s-wave pairing in the superconducting phase. Meanwhile there is a possibility that the Zn impurity may selectively enter into the insulting phase.