Mesoscopic flux jumps in MgB2 films visualized by magneto-optical imaging

TL;DR

This study visualizes mesoscopic and dendritic flux jumps in MgB2 superconducting films using magneto-optical imaging, revealing their size, distribution, and possible thermo-magnetic origin at low temperatures.

Contribution

First spatially resolved observation of mesoscopic flux jumps in MgB2 films, linking flux behavior to thermo-magnetic instability.

Findings

Flux jumps occur randomly along the flux front below 10 K.

Mesoscopic jumps involve 50-10,000 vortices, dendritic jumps involve millions.

Both jump types are likely caused by thermo-magnetic instability.

Abstract

We report on the first spatially resolved observation of mesoscopic flux jumps in superconducting films. Magneto-optical imaging was used to visualize the flux penetration in MgB2 films subjected to a slowly varying perpendicular field. Below 10 K, flux jumps with typical size 10-20 microns and regular shape are found to occur at random locations along the flux front. The total number of vortices participating in one jump is varying between 50 and 10000. Simultaneously, big dendritic jumps with dimensions comparable to the sample size (10^6-10^8 vortices) are also found in this temperature range. We believe that both types of jumps result from thermo-magnetic instability.