Single Impurity Problem in Iron-Pnictide Superconductors

TL;DR

This paper investigates the effects of non-magnetic impurities on iron-pnictide superconductors using a five-orbital BdG model, revealing bound states that help distinguish between s$_{+-}$ and s$_{++}$ pairing symmetries.

Contribution

The study develops a five-orbital model for BdG analysis of impurity effects, enabling differentiation of superconducting states in iron-pnictides.

Findings

Nearly zero-energy bound state at specific impurity potential.

Bound states stick to gap edges in the unitary limit.

Multiple peak structures due to multi-orbital effects.

Abstract

Single impurity problem in iron-pnictide superconductors is investigated by solving Bogoliubov-de Gennes (BdG) equation in the five-orbital model, which enables us to distinguish s$_{+-}$ and s$_{++}$ superconducting states. We construct a five-orbital model suitable to BdG analysis. This model reproduces the results of random phase approximation in the uniform case. Using this model, we study the local density of states around a non-magnetic impurity and discuss the bound-state peak structure, which can be used for distinguishing s$_{+-}$ and s$_{++}$ states. A bound state with nearly zero-energy is found for the impurity potential $I\sim 1.0$ eV, while the bound state peaks stick to the gap edge in the unitary limit. Novel multiple peak structure originated from the multi-orbital nature of the iron pnictides is also found.