Experimental study of intrinsic multiple Andreev reflections effect in GdO(F)FeAs superconductor array junctions

TL;DR

This study observes intrinsic multiple Andreev reflections in GdO(F)FeAs superconductor arrays, enabling precise measurement of superconducting gaps and revealing strong electron-boson coupling.

Contribution

First observation of IMARE in superconductor arrays, improving accuracy of superconducting parameter determination and confirming strong coupling in GdO(F)FeAs.

Findings

Superconducting gaps: Δ_L = 11 ± 1.1 meV, Δ_S = 2.6 ± 0.4 meV.

Enhanced spectral features in arrays compared to single contacts.

BCS ratio indicates strong electron-boson coupling.

Abstract

We report the first observation of the intrinsic multiple Andreev reflections effect (IMARE) in S-n-S-...-S-arrays (S = superconductor, n = normal metal) formed by "break-junction" technique in GdO(F)FeAs superconductor (Tc = 48 - 53 K). We show that superconducting gap peculiarities at dI/dV-spectra sharpen dramatically in the arrays as compared with that in the single-contact spectra; this enables to improve significantly accuracy of the bulk superconducting parameters determination. Using IMARE, we determined the large and the small gap values \Delta_L = 11 +- 1.1 meV and \Delta_S = 2.6 +- 0.4 meV. The BCS-ratio 2\Delta_L/kTc^{local} = 5.0 - 5.9 > 3.52 (Tc^{local} is the contact area critical temperature) evidences for a strong electron-boson coupling. The results obtained agree well with our previous data by Andreev spectroscopy for single SnS-contacts.