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

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.

On Ginzburg-Landau Vortices of Superconducting Thin Films

In this paper, we discuss the vortex structure of the superconducting thin films placed in a magnetic field. We show that the global minimizer of the functional modelling the superconducting thin films has a bounded number of vortices when the applied magnetic field hex 〈 Hc1 ＋ K log ｜ logε｜ where Hc1 is the lower critical field of the film obtained by Ding and Du in SIAM J. Math. Anal., 2002. The locations of the vortices are also given.

Degradation Mechanism of the Superconducting Transition Temperature in Nb Thin Films

Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is contrary to the prevailing understanding based on the interplay between proximity, localization, and lifetime broadening. Our study indicates that the decrease of Tc can be interpreted by the combined effects of electron-phonon coupling parameter λ and the defect scattering rate pw, being uniquely determined by their ratio λ/ρw. Other factors such as film thickness and irradiation do not produce additional effects beyond these two parameters.