Estimation of intraband and interband relative coupling constants from temperature dependences of the order parameter for two-gap superconductors

TL;DR

This paper measures the temperature dependence of superconducting gaps in Fe-based superconductors and MgB2, using a two-gap model to estimate intraband and interband coupling constants, revealing strong intraband coupling in large-gap bands.

Contribution

It introduces a method to directly determine relative coupling constants from temperature-dependent gap measurements in two-gap superconductors.

Findings

Strong intraband coupling in large-gap bands.

Weak interband coupling across studied superconductors.

Quantitative estimates of coupling constants and BCS ratios.

Abstract

We present temperature dependences of the large and the small superconducting gaps measured directly by SnS-Andreev spectroscopy in various Fe-based superconductors and MgB$_2$. The experimental $\Delta_{L,S}(T)$ are well-fitted with a two-gap model based on Moskalenko and Suhl system of equations (supplemented with a BCS-integral renormalization). From the the fitting procedure, we estimate the key attribute of superconducting state \textemdash relative electron-boson coupling constants and eigen BCS-ratios for both condensates. Our results evidence for a driving role of a strong intraband coupling in the bands with the large gap, whereas interband coupling is rather weak for all the superconductors under study.