Evolution of quasiparticle states with and without a Zn-impurity in doped 122 iron pnictides

TL;DR

This study uses a two-orbital model to analyze how quasiparticle states and local density of states evolve with doping and impurity presence in 122 iron pnictides, revealing insights into superconducting gaps and impurity effects.

Contribution

It demonstrates the applicability of a minimal two-orbital model to describe LDOS and impurity effects in doped 122 iron pnictides, aligning with more complex models.

Findings

Identification of two superconducting gaps in doped samples

Qualitative agreement of impurity LDOS with five-orbital models

Prediction of impurity-induced in-gap resonance states

Abstract

Based on a minimal two-orbital model [Tai {\it et al.}, Europhys. Lett. \textbf{103}, 67001 (2013)], which captures the canonical electron-hole-doping phase diagram of the iron-pnictide BaFe$_{2}$As$_{2}$, we study the evolution of quasiparticle states as a function of doping using the Bogoliubov-de Gennes equations with and without a single impurity. Analyzing the density of states of uniformly doped samples, we are able to identify the origin of the two superconducting gaps observed in optimally hole- or electron-doped systems. The local density of states (LDOS) is then examined near a single impurity in samples without antiferromagnetic order. The qualitative features of our results near the single impurity are consistent with a work based on a five-orbital model[K. Toshikaze {\it et al.}, J. Phys. Soc. Jpn. \textbf{79}, 083704 (2010)]. This further supports the validity of our two-orbital model in dealing with LDOS in the single-impurity problem. Finally, we investigate the evolution of the LDOS with doping near a single impurity in the unitary or strong scattering limit, such as Zn replacing Fe. The positions of the ingap resonance peaks exhibited in our LDOS may indirectly reflect the evolution of the Fermi surface topology according to the phase diagram. Our prediction of ingap states and the evolution of the LDOS near a strong scattering single impurity can be validated by experiments probing the local quasiparticle spectrum.