Recent experiments on Zn-substituted 122-type iron-based superconductors (FeSCs) at electron- and hole-doped regions provide us with a testing ground for understanding the effect of Zn impurities in these systems. Our first-principles calculations of the electronic structure reveal that the Zn $3d$ orbitals are far below the Fermi level and are chemically inactive, while the Zn $4s$ orbital is partially occupied and its wave function overlaps with the $3d$ orbitals of neighboring Fe ions. This suggests that the impurity effect originates 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.

• Received 16 November 2015
• Revised 4 April 2016

DOI:https://doi.org/10.1103/PhysRevB.93.144510