Dynamic Study of the Environmental Impact on Gap Relaxation Time in NbTi Superconducting Wire

We have studied non-equilibrium states in NbTi films deposited on fused silica under different surrounding conditions using electrical current pulses. When the applied current exceeds the depairing current, a voltage response is observed after a characteristic delay time. Although the sample dimensions are much larger than the coherence length, the localized micro-metric region formed corresponds to a hotspot. The delay times are quantitatively described using the Time-Dependent Ginzburg–Landau (TDGL) theory of M. Tinkham, enabling the determination of filament cooling times for the same sample in both liquid helium and vacuum. We find cooling times of about ns in vacuum and ns in liquid helium. These results demonstrate that liquid helium has only a minor effect on the film cooling time, with most of the heat being transferred into the substrate via phonons.