Discontinuous hotspot growth related to the thermal healing length in superconducting NbN microstrips

Abstract

Electrical transport measurements were performed on NbN multicontact microstrips in order to investigate the non-equilibrium dissipative states in highly disordered granular superconducting nanostructures. By applying a dc voltage-bias, a peculiar discontinuous normal phase propagation was observed in a current interval well below the switching point. These stabilized resistive states are explained within the framework of a localized normal hotspot maintained by Joule heating. The thermal healing length of our NbN microstrips is estimated by taking into account both kinds of heat transfer (i.e. by conduction within the microstrip and by surface heat transfer through the substrate). It appears that the estimated healing length properly matches the length associated with a normal region across the whole width and whose resistance is given by the difference of resistance between two nearest intermediate dissipative states as observed in the voltage-biased curves. © 2010 IOP Publishing Ltd.