Superconductivity suppression of Ba0.5K0.5Fe2-2xM2xAs2 single crystals by substitution of transition metal (M = Mn, Ru, Co, Ni, Cu, and Zn)

We investigated the doping effects of magnetic and nonmagnetic impurities in single-crystalline p-type Ba0.5K0.5Fe2-2xM2xAs2 (M = Mn, Ru, Co, Ni, Cu, and Zn) superconductors. The superconductivity is maintained robustly with the impurity Ru, and weakly with the impurities Mn, Co, Ni, Cu, and Zn. However, the present T-c suppression rate of both magnetic and nonmagnetic impurities remains much lower than what was expected for the s(+/-)-wave model. The temperature dependence of resistivity data shows an obvious low-T upturn for the crystals doped with high levels of impurity, which is due to the occurrence of localization. Thus, the relatively weak T-c suppression effect from Mn, Co, Ni, Cu, and Zn is considered to be a result of localization rather than the pair-breaking effect in the s(+/-)-wave model.