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

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 ($Delta_L < varepsilon_0 < Delta_L +Delta_S$).