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

TL;DR

This study investigates how realistic finite-size impurities affect the superconducting transition temperature (Tc) in Fe-based superconductors, revealing the fragility of the $s_$-wave state against impurities using a five-orbital tight-binding model.

Contribution

It introduces realistic impurity models with non-local effects and demonstrates the fragility of the $s_$-wave state against impurities based on first-principles parameters.

Findings

Superconductivity is destroyed by small residual resistivity levels.

The fragility of the $s_$-wave state is consistent across different impurity models.

Impurity-induced non-local orbital order impacts the superconducting state.

Abstract

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 ($s_\pm$-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 $s_\pm$-wave state is very fragile against impurities: The superconductivity with $T_{c0}=30K$ is destroyed by introducing small residual resistivity $\rho_0^{cr} = 5z^{-1} ~ 10z^{-1} [\mu\Omega cm]$ ($z^{-1} = m^*/m$ 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.