Suppression of flux avalanches in YBCO superconducting thin films by coating metal investigated using magneto-optical imaging

Abstract

Flux avalanches, prevalently existing in superconducting thin films, can cause catastrophic breakdowns of electromagnetic properties and even irreversible damage to superconducting materials. Metal coating is an effective way to suppress the flux avalanches in superconducting thin films. Nevertheless, it is difficult to reveal the suppression mechanisms due to the challenge of effectively separating the simultaneous eddy currents and heat exchange in the metal coating. In this work, the eddy currents and heat exchange in the Ag metal coating are separated by setting a thermal insulation layer, and its inhibiting effect on the flux avalanches of the YBCO superconducting thin films is elucidated. The results indicate that eddy currents play an important part in suppressing magnetic flux avalanches, and their effect strengthens with increasing Ag thickness. Meanwhile, employing the double-exposure method, the flux avalanche velocity of YBCO superconducting thin films was measured, revealing a significant decrease in the magnetic flux avalanche velocity due to suppression by eddy currents. Moreover, a theoretical model was established to investigate the influence of eddy currents on the motion of a single vortex, and the calculated results showed good agreement with the experiments. These findings provide a better understanding of the flux avalanches and their suppression in YBCO superconducting thin films.