Enhanced flux line pinning by substrate induced defects in YBCO thin films

The critical current density of YBa2Cu3O7-delta (YBCO) thin films strongly depends on the surface properties of the substrate. We modify the surface of SrTiO3 single crystalline substrates using a 30 keV focussed beam of gallium ions. After characterizing the created patterns on the substrate by atomic force microscopy, thin films of optimally doped YBCO are deposited by pulsed laser deposition. By means of quantitative magnetooptical measurements it is found that a proper irradiation process can enhance the critical current density of the deposited superconducting film. The film growth on the irradiated substrate can lead to a higher and controlled defect density and thus to a modified distribution of effective flux line pinning sites in the superconductor. (C) 2004 Elsevier B.V. All rights reserved.