Current Assisted, Thermally Activated Flux Liberation in Ultrathin Nanopatterned NbN Superconducting Meander Structures

TL;DR

This study investigates fluctuation phenomena in ultrathin NbN superconducting nanowires, revealing thermally activated vortex dynamics as the primary mechanism behind flux liberation and voltage pulses near the critical current.

Contribution

It demonstrates that thermally excited vortices, rather than other models, best explain fluctuation-induced voltage pulses in NbN nanowires at low temperatures.

Findings

Thermally excited vortices explain flux liberation in NbN nanowires.

Vortex-antivortex unbinding and edge barrier overcoming are key mechanisms.

Experimental data aligns with vortex-based models over other fluctuation theories.

Abstract

We present results from an extensive study of fluctuation phenomena in superconducting nanowires made from sputtered NbN. Nanoscale wires were fabricated in form of a meander and operated at a constant temperature T~0.4Tc(0). The superconducting state is driven close to the electronic phase transition by a high bias current near the critical one. Fluctuations of sufficient strength temporarily drive a section of the meander structure into the normal conducting state, which can be registered as a voltage pulse of nanosecond duration. We considered three different models (vortex-antivortex pairs, vortex edge barriers and phase slip centers) to explain the experimental data. Only thermally excited vortices, either via unbinding of vortex-antivortex pairs or vortices overcoming the edge barrier, lead to a satisfactory and consistent description for all measurements.