Anisotropic flux pinning in thin YBCO-films by substrate modifications

The magnetooptical Faraday effect is an excellent tool to investigate the spatially resolved flux density distribution and, by a numerical inversion of the Biot-Savart law, the local current density in a superconducting film with a spatial resolution better than 10 mu m [Ch. Jooss, R. Warthmann, A. Forkl, H. Kronmuller, Physica C 299 (1998) 215]. irradiating the surface of SrTiO3(001) substrates with a focused ion beam in a line pattern lends to an anisotropy of the flux and current density distribution in a well-defined area. While we measure an enhancement of j(c) parallel to the lines, a reduction of the value of the current perpendicular to the lines is found. This is in qualitative agreement with experiments on YBCO films grown on vicinal substrate surfaces [T. Haage, J. Zegenhagen, J.Q. Li, H.-U. Habermeier, M. Cardona, Ch. Jooss, R. Warthmann, A. Forkl. H. Kronmuller, Phys. Rev. B 56 (1997) 8404] and based on the data gained on these systems, a pinning model for the films on the irradiated substrates is suggested. (C) 2000 Elsevier Science B.V. All rights reserved.