Strong electron-phonon interaction in multiband superconductors

TL;DR

This paper investigates how strong electron-phonon interactions and anisotropy in multiband superconductors influence the critical temperature and order parameters, revealing pair-breaking effects that limit superconducting performance.

Contribution

It introduces a multiband model to analyze anisotropic strong coupling effects, highlighting the role of soft phonon modes as pair-breakers and their impact on the critical temperature.

Findings

Strong coupling causes pair-breaking via interband interactions.

Soft phonon modes act like impurities, affecting superconductivity.

Order parameters in different bands tend to become equal.

Abstract

We discuss the effects of anisotropy on superconducting critical temperature and order parameter in a strongly coupled regime. The multiband representation is used as a model for anisotropy. We show that strong coupling effects in multiband superconductors lead to pair-breaking due to interband coupling because soft phonon modes play the same role as usual impurities. This effect makes the order parameters in different bands equal to each other and limits the upper bound on critical temperature.