Effect of realistic finite-size impurities on T_c in Fe-based superconductors based on the five-orbital tight-binding model

We present a systematic study of the impurity effect on T_c in Fe-based superconductors, assuming that the sign-reversal s-wave state due to interpocket repulsion (the s_±-wave state) is realized. For this purpose, we introduce several realistic impurity models with nonlocal modifications of potentials and hopping integrals around the impurity site. When we use the impurity model parameters for 3d- and 4d-impurity atoms derived from the recent first-principles study by Nakamura, we find that the s _±-wave state is very fragile against impurities: The superconductivity without impurities T_c0=30K is destroyed by introducing small residual resistivity ρ0cr=5z^-1-10z ^-1μΩcm (z^-1=m^*/m, being the mass-enhancement factor), consistent with the previous theoretical study for the on-site impurity model by Onari and Kontani. This result is essentially unchanged for different nonlocal impurity models with realistic parameters. We also discuss the effect of the impurity-induced non-local-orbital order on the superconducting state.