Reentrant stability of superconducting films

TL;DR

This paper explains the reentrant stability of superconducting NbN films under increasing magnetic fields, attributing it to a thermomagnetic mechanism related to the critical current density's behavior.

Contribution

It provides experimental evidence and a quantitative explanation for the reentrant stability phenomenon in superconducting films using a thermomagnetic model.

Findings

Reentrant stability occurs at specific threshold fields.

The stability is linked to the decreasing critical current density.

Experimental results agree with the thermomagnetic model.

Abstract

We propose a mechanism responsible for the abrupt vanishing of the dendritic flux instability found in many superconducting films when an increasing magnetic field is applied. The onset of flux avalanches and the subsequent reentrance of stability in NbN films was investigated using magneto-optical imaging, and the threshold fields were measured as functions of critical current density, $j_c$. The results are explained with excellent quantitative agreement by a thermomagnetic model published recently, Phys. Rev. B73, 014512 (2006), showing that the reentrant stability is a direct consequence of a monotonously decreasing $j_c$ versus field.