Multigap Superconductivity in GdFeAsO$_{0.88}$ Evidenced by SnS-Andreev Spectroscopy

TL;DR

This study uses Andreev spectroscopy to investigate multigap superconductivity in GdFeAsO$_{0.88}$, revealing two superconducting gaps with temperature behaviors deviating from BCS theory, indicating complex interband interactions.

Contribution

First direct measurement of two superconducting gaps in GdFeAsO$_{0.88}$ using IMARE spectroscopy, highlighting the importance of k-space proximity effects.

Findings

Identification of two distinct superconducting gaps.

Temperature dependence deviates from BCS predictions.

Evidence of internal proximity effect between condensates.

Abstract

Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy we studied superconducting properties of nearly optimal oxygen-deficient GdFeAsO$_{0.88}$ polycrystalline samples (bulk critical temperatures $T_C^{bulk} = 49 \div 52$\,K). Temperature dependences for two superconducting gaps $\Delta_{L,S}(T)$ ($T_C^{local} = 48 \div 50$\,K) have been measured in the range from 4.2 to 50\,K. The $\Delta_{L,S}(T)$ dependences were found to deviate from the BCS-like function; this suggests an importance of the $k$-space (internal) proximity effect between the two condensates.