Superconducting fluctuations and quasiparticle recombination times in disordered Mo2N thin films

Abstract

Disordered Mo2N thin films exhibit a superconducting transition up to 7.7 K, together with a weak metal–insulator crossover and positive magnetoresistance emerging already near 30 K, well above the critical temperature (Tc). This ≈ 30 K signature persists in both thick and ultrathin films, and even becomes more pronounced in the ultrathin limit, indicating an atomic-scale origin largely insensitive to thickness. The magnetoresistance is nearly isotropic with respect to field orientation and persists up to 16 T, pointing to unexpectedly robust superconducting fluctuations extending far above Tc. For a film with Tc = 7.7 K, by fitting the field-dependent conductance within the weak-localization plus Maki–Thompson framework for T > 8 K, we extract the inelastic scattering time (τi), which is ≈ 5 ps near Tc and decreases systematically with temperature. A decomposition of the inelastic rate reveals electron–electron and electron–phonon channels corresponding to characteristic times of ≈ 10 ps and ≈ 50 ps, respectively. These values agree with previous estimates from vortex critical-velocity measurements and underscore molybdenum nitride as a promising platform for fast radiation detectors.