Observation of Transient Overcritical Currents in YBCO Thin Films using High-Speed Magneto-Optical Imaging and Dynamic Current Mapping

TL;DR

This study reveals transient overcritical currents in YBCO thin films during magnetic field ramps, using high-speed magneto-optical imaging to uncover novel dynamic behaviors and transitions in supercurrent evolution.

Contribution

It introduces a new real-time imaging method to observe and analyze transient supercurrent peaks exceeding critical current limits in superconducting films.

Findings

Detection of supercritical current peaks near edges during field ramp-up

Observation of a transition from increasing peaks to relaxation behavior

Long-term current distribution aligns with Kim-model profile

Abstract

The dynamics of transient current distributions in superconducting YBCO thin films were investigated during and immediately following an external field ramp, using high-speed (real-time) Magneto-Optical Imaging and calculation of dynamic current profiles. A number of qualitatively unique and previously unobserved features are seen in this novel analysis of the evolution of supercurrent during penetration. As magnetic field ramps up from zero, the dynamic current profile is characterized by strong peaks, the magnitude of which exceed the conventional critical current density (as determined from static current profiles). These peaks develop close to the sample edges, initially resembling screening currents but quickly growing in intensity as the external field increases. A discontinuity in field and current behaviour is newly observed, indicating a novel transition from increasing peak current toward relaxation behaviour. After this transition, the current peaks move toward the centre of the sample while reducing in intensity as magnetic vortices penetrate inward. This motion slows exponentially with time, with the current distribution in the long-time limit reducing to the expected Kim-model profile.