Radiation damages and flux pinning in YBa2Cu3O7 thin films

Abstract

We were able to increase the critical current density (Jc) and implicitly, enhance the flux pinning in high quality epitaxial YBCO thin films by 200 keV proton irradiation. The critical temperature (Tc) of the film does not change until radiation-induced localized defects begin to overlap over distances to the extent of a coherence length. The point defect induced by radiation damage or the radiation induced weak center (RWC) is believed to be responsible for the observed flux pinning enhancement. The self-field of the transport current transforms the RWCs into pinning centers. Compared to the bulk materials, the much lower Jc enhancement factor observed after irradiation of the thin films is due to the already very strong pinning force of the pinning defects in thin films. The extra pinning force of radiation defects is just a small perturbation on top of a large background.