Local threshold field for dendritic instability in superconducting MgB2 films

TL;DR

This study investigates dendritic flux penetration in MgB2 superconducting films, revealing a local threshold magnetic field that controls dendrite formation, contrasting bulk superconductor behavior.

Contribution

It identifies a specific local threshold field for dendritic instability in MgB2 films, highlighting differences from bulk superconductor flux jumps.

Findings

Local threshold field near 12 mT at 4 K

Dendritic flux penetration occurs abruptly

Threshold field controls dendrite nucleation and termination

Abstract

Using magneto-optical imaging the phenomenon of dendritic flux penetration in superconducting films was studied. Flux dendrites were abruptly formed in a 300 nm thick film of MgB2 by applying a perpendicular magnetic field. Detailed measurements of flux density distributions show that there exists a local threshold field controlling the nucleation and termination of the dendritic growth. At 4 K the local threshold field is close to 12 mT in this sample, where the critical current density is 10^7 A/cm^2. The dendritic instability in thin films is believed to be of thermo-magnetic origin, but the existence of a local threshold field, and its small value are features that distinctly contrast the thermo-magnetic instability (flux jumps) in bulk superconductors.