Study of the Two-Gap Superconductivity in GdO(F)FeAs by ScS-Andreev Spectroscopy

TL;DR

This study investigates two-gap superconductivity in GdO(F)FeAs using ScS-Andreev spectroscopy, revealing two distinct gaps and supporting strong coupling as the mechanism behind its high critical temperature.

Contribution

It provides direct experimental evidence of two-gap superconductivity in GdO(F)FeAs and analyzes the temperature dependence of the gaps, highlighting the intrinsic proximity effect.

Findings

Two superconducting gaps observed: Delta_L = 10.5 meV and Delta_S = 2.3 meV.

The large gap ratio supports a strong coupling mechanism.

Temperature dependence indicates an intrinsic proximity effect between condensates.

Abstract

Current-voltage characteristics and dynamic conductance of the superconductor - constriction - superconductor junctions in GdO(F)FeAs polycrystalline samples with critical temperatures Tc^local = 46 - 53 K were investigated. Two superconducting gaps, the large Delta_L = 10.5 +- 2 meV, and the small one Delta_S = 2.3 +- 0.4 meV were clearly observed at T = 4.2 K. The 2Delta_L/kTc^local = 5.5 +- 1 ratio gives support to the strong coupling mechanism which is responsible for the high Tc value. Temperature dependence of the large gap Delta_L(T) indicates the presence of intrinsic proximity effect (in k-space) between two superconducting condensates.