Effects of single- and multi-substituted Zn ions in doped-122 type iron-based superconductors

TL;DR

This study investigates how Zn impurities affect superconductivity in 122-type iron-based superconductors, revealing that Zn 4s orbitals, not 3d orbitals, are responsible for impurity effects, with results aligning with experiments.

Contribution

The paper introduces a phenomenological two-orbital model and self-consistent calculations to explain Zn impurity effects in doped FeSCs, highlighting the role of Zn 4s orbitals.

Findings

Zn 3d orbitals are inactive and far below the Fermi level.

Zn 4s orbitals overlap with Fe 3d orbitals, influencing impurity effects.

Results agree qualitatively with experimental observations.

Abstract

Recent experiments on Zn-substituted 122-type iron-based superconductors (FeSCs) at electron- and hole- doped region provide us with a testing ground for understanding the effect of Zn impurities in these systems. Our first-principle calculations of the electronic structure reveal that the Zn 3d orbitals are far below the Fermi level and chemically inactive, while the Zn 4s-orbital is partially occupied and its wave function overlapping with those 3d-orbitals of neighboring Fe-ions. This suggests that the impurity effect is originating in the Zn 4s-orbital, not its 3d-orbitals. Employing a phenomenological two-orbital lattice model for 122-FeSCs and the self-consistent Bogoliubov-de Gennes equations, we study how the Zn-impurities suppress the superconductivity in electron- and hole- doped compounds. Our obtained results qualitatively agree with the experimental measurements.