Effect of Impurities with Internal Structure on Multiband Superconductors - Possible Enhancement of Transition Temperature -

TL;DR

This paper investigates how impurities with internal structures can enhance the transition temperature in multiband superconductors, focusing on impurity scattering effects and their influence on different pairing symmetries.

Contribution

It introduces a model for impurity-mediated pairing in multiband superconductors, highlighting conditions under which impurity scattering can enhance $T_c$ for different pairing states.

Findings

Impurity scattering can favor either $s_{++}$ or $s_$-wave states.

Magnetic interband scattering can enhance $T_c$ under certain impurity configurations.

The model is applied to Pr impurities in LaOs$_4$Sb$_{12}$, suggesting possible $T_c$ enhancement.

Abstract

We study inelastic (dynamical) impurity scattering effects in two-band superconductors with the same ($s_{++}$ wave) or different ($s_\pm$ wave) sign order parameters. We focus on the enhancement of the superconducting transition temperature $T_{\rm c}$ by magnetic interband scattering with the interchange of crystal-field singlet ground and multiplet excited states. Either the $s_{++}$-wave or $s_\pm$-wave state is favored by the impurity-mediated pairing, which depends on the magnetic and nonmagnetic scattering strengths derived from the hybridization of the impurity states with the conduction bands. The details are examined for the singlet-triplet configuration that is suggestive of Pr impurities in the skutterudite superconductor LaOs$_4$Sb$_{12}$.