Superconducting Order Parameter and Bosonic Mode in Hydrogen-Substituted NdFeAsO$_{0.6}$H$_{0.36}$ Revealed by Multiple Andreev Reflection Spectroscopy

TL;DR

This study uses multiple Andreev reflection spectroscopy to measure superconducting gaps and bosonic modes in hydrogen-substituted NdFeAsO, revealing two distinct order parameters and their temperature dependence.

Contribution

First direct measurement of two bulk superconducting gaps and bosonic mode coupling in NdFeAsO$_{0.6}$H$_{0.36}$ using IMARE spectroscopy.

Findings

Large gap $oxed{ ext{~10.4 meV}}$ identified

Small gap $oxed{ ext{~1.8 meV}}$ identified

Bosonic mode energy $oxed{ ext{10.5-11.0 meV}}$ observed

Abstract

Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we studied ballistic superconductor - normal metal - superconductor (SnS) contacts in layered oxypnictide superconductors NdFeAsO$_{0.6}$H$_{0.36}$ with critical temperatures $T_c = 45-48$ K. We directly determined the magnitude of two bulk superconducting order parameters, the large gap $\Delta_L \approx 10.4$ meV, and a possible small gap $\Delta_S \approx 1.8$ meV, and their temperature dependence. Additionally, a resonant coupling with a characteristic bosonic mode was observed. The boson energy at 4.2 K, $\varepsilon_0 = 10.5-11.0$ meV being less than the indirect gap ($\Delta_L < \varepsilon_0 < \Delta_L +\Delta_S$).