Impurity effects on the Fe-based superconductor A(Fe1−yCoy)2As2 (A=Ba and Sr)

In this study, we address the superconductivity of the Zn- and Mn-doped Fe-based superconductors Ba(Fe1−x−yMxCoy)2As2 (M=Zn and Mn) and Sr(Fe0.9−xZnxCo0.1)2As2. The impurity is successfully doped into the lattice of the superconductors under a high-pressure heating condition, resulting in a continuous decrease in T c toward zero. Not only the optimally doped, but also the under- and over-doped superconducting states show a noticeable decrease in T c as a function of the Zn concentration. The rate of decrease, however, is not as large as the theoretical value expected from the s ± -wave model, suggesting that this model is unlikely to be applied to the superconductivity of the present 122 system.