Effect of realistic finite-size impurities on Tc in Fe-based superconductors based on the five-orbital tight-binding model
We present a systematic study of the impurity effect on Tc in Fe-based superconductors, assuming that the sign-reversal s-wave state due to inter-pocket repulsion ($s_±$-wave state) is realized. For this purpose, we introduce several realistic impurity models with non-local 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 principle study by Nakamura et al., we find that the $s_±$-wave state is very fragile against impurities: The superconductivity with $T_c0=30K$ is destroyed by introducing small residual resistivity $ρ_0^cr = 5z^-1 ~ 10z^-1 [μΩ cm]$ ($z^-1 = m^*/m$ being the mass-enhancement factor), consistently with the previous theoretical study for the on-site impurity model by Onari and Kontani. This result is essentially unchanged for different non-local impurity models with realistic parameters. We also discuss the effect of the impurity-induced non-local orbital order on the superconducting state.