Probing the Quasiparticle Relaxation Time in Ultrathin NbN Microbridges via Larkin–Ovchinnikov Instability Near Tc

We investigate the Larkin–Ovchinnikov instability in epitaxial NbN microbridges, focusing on the impact of structural homogeneity on vortex dissipation. Analyzing current–voltage curves under various magnetic fields and temperatures reveals vortex velocities up to 6 km/s. These velocities decrease with an increasing magnetic field and stabilize into a plateau near the critical temperature. The extracted recombination times (τ) range around 10 ps and decrease with temperature, indicating the involvement of thermally activated phonons. Furthermore, thinner films show shorter τ values, emphasizing the influence of film thickness on vortex dynamics. Comparison with the existing literature underscores the significance of disorder and surface roughness in determining vortex velocity. Our findings offer valuable insights into vortex behavior in high-quality thin films, with potential implications for advancing superconducting technologies.