Measurement of Thermal relaxation time of superconducting strips deduced from the nucleation of current-induced Hot spots (MTRS)

We propose to use a sample with different layers; an active layer consists of NbTiN superconducting thin filament grown on sapphire substrate. A hotspot is generated in the filament due the application of an electrical current pulse exceeding the critical current Ic. A SiOx insulating layer of few nanometers is partially deposited on top of the superconducting layer. A germanium layer is grown on top of the insulating layer, it serves to record the change of temperature reached at the center of the hotspot. In superconducting state, where no bias current is applied, Ge thermometer is calibrated. In this proposal, first, we aim at the measurement of temperature reached at the center of the hotspot dissipation due an over-critical current in NbTiN filament. The heat generated inside the normal zone is evacuated toward the substrate and increases the germanium resistance. Second, from the two-power expression (the one dissipated inside the normal hotspot and the evacuated one) the heat escape time is deduced. It will be compared to the value deduced from dynamical approach (or temporal analysis) of PSC or HS created by an electrical current, where it provides us directly with the phonon escape time, by fitting the experimental data with the TDGL equation. It is an importance major relevant parameter for the rest time of the SSPD.