Statistics of localized phase slips in tunable width planar point contacts

Xavier D.A Baumans,Joris Van De Vondel,Francesco Tafuri,Vyacheslav S Zharinov,Sylvain Blanco Alvarez,Davide Massarotti,Jeroen E Scheerder,Jérémy Brisbois,Eline Raymenants,Alejandro V Silhanek,Ewald Janssens,Roberta Caruso,Victor V Moshchalkov

doi:10.1038/srep44569

Abstract

The main dissipation mechanism in superconducting nanowires arises from phase slips. Thus far, most of the studies focus on long nanowires where coexisting events appear randomly along the nanowire. In the present work we investigate highly confined phase slips at the contact point of two superconducting leads. Profiting from the high current crowding at this spot, we are able to shrink in-situ the nanoconstriction. This procedure allows us to investigate, in the very same sample, thermally activated phase slips and the probability density function of the switching current Isw needed to trigger an avalanche of events. Furthermore, for an applied current larger than Isw, we unveil the existence of two distinct thermal regimes. One corresponding to efficient heat removal where the constriction and bath temperatures remain close to each other, and another one in which the constriction temperature can be substantially larger than the bath temperature leading to the formation of a hot spot. Considering that the switching current distribution depends on the exact thermal properties of the sample, the identification of different thermal regimes is of utmost importance for properly interpreting the dissipation mechanisms in narrow point contacts.

Highlights

Real systems possess certain thermal inertia implying a finite lifetime τ ~ 0.1 ns of the footprints left by a phase slip
A weak self-heating regime where the heat removal is rather efficient and the superconducting constriction switches to the normal state in two steps when increasing current
A strong self-heating regime where the transition to the normal state corresponds to a single abrupt jump

Summary

Introduction

Real systems possess certain thermal inertia implying a finite lifetime τ ~ 0.1 ns of the footprints left by a phase slip. If heat removal is absent (τ →∞), it may happen that a single event is able to trigger a thermal runaway. In this case the width of the distribution reflects the stochasticity of individual events. If we were able to ramp up the current with an infinite rate, i.e. much faster than the attempt frequency of single events, we should attain the critical current of the system[14] In this limit, the information concerning the activation mechanism is lost. The statistical distribution of Isw at finite sweep rates encodes information about the main physical mechanism triggering the events and whether it is of quantum or thermal origin. The physics addressed in the present manuscript might provide a new approach for understanding the statistics of flux avalanche triggering of thermomagnetic origin in thin superconducting films or the escape distribution for magnetization reversal in small particles, sampling events distribution might be harder in these systems

Methods

Results

Conclusion