Impurities in multiband superconductors

TL;DR

This paper investigates how impurities affect multiband superconductors, especially iron-based pnictides and chalcogenides, revealing impurity-induced transitions between different superconducting states.

Contribution

It provides a detailed analysis of impurity effects on unconventional multiband superconductors, highlighting impurity-induced state transitions and their observable consequences.

Findings

Disorder can induce transitions between $s_$ and $s_{++}$ states.

Both magnetic and nonmagnetic impurities influence superconducting symmetry.

Observable effects include changes in superconducting properties due to impurity-induced transitions.

Abstract

Disorder - impurities and defects violating an ideal order - is always present in solids. It can result in interesting and sometimes unexpected effects in multiband superconductors. Especially if the superconductivity is unconventional thus having other than the usual s-wave symmetry. This paper uses the examples of iron-based pnictides and chalcogenides to examine how both nonmagnetic and magnetic impurities affect superconducting states with $s_\pm$ and $s_{++}$ order parameters. We show that disorder causes the transitions between $s_\pm$ and $s_{++}$ states and examine observable effects these transitions can produce.