Dissipative States Induced by Current Pulse in NbTi Superconducting Filaments

 

We investigated the induced non-equilibrium states in superconducting NbTi wires using short electrical current pulse technique. The energy dissipation occurs once the current pulse amplitude exceeds the depairing current (Ic). For a wire with a demension larger than the coherence length (ζ), vortex and antivortex trains are generated and then flow in transverse direction to the applied current and opposite to each other so that they annihilate at the center of the filament to create phase slip lines. This is considered as a metastable state in which the order parameter value oscillates between zero and one (a mixture of normal and superconducting states).  A pure normal dissipative local area referred to as a hotspot appears in the filament where the total collapse of the superductivity occurs.  As a result, a voltage appears after certain delay time td marking the initiation of energy dissipation. The thermal relaxation time was extracted from fitting the experimental data with the Time-Dependent Ginzburg-Landau (TDGL) theory due to M. Tinkham at 4 K.