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 ${\mathrm{\Delta }}_L\approx 10.4$ meV, and a possible small gap ${\mathrm{\Delta }}_S\approx 1.8$ meV, and their temperature dependence. Additionally, a resonant coupling with a characteristic bosonic mode was observed. The boson energy at 4.2 K, ${\epsilon }_0=10.5-11.0$ meV being less than the indirect gap ($\Delta_L < \varepsilon_0 < \Delta_L +\Delta_S$).