Critical currents in vicinal YBa2Cu3O7-δ films -: art. no. 214508

Most measurements of critical current densities in YBa2Cu3O7-delta thin films to date have been performed on films where the c axis is grown normal to the film surface. With such films, the analysis of the dependence of the critical current, j(c), on the magnetic field angle is complex. The effects of extrinsic contributions to the angular field dependence of j(c), such as the measurement geometry and disposition of pinning centers, are convoluted with those intrinsically due to the anisotropy of the material. As a consequence of this, it is difficult to distinguish between proposed flux line lattice structure models on the basis of angular critical current density measurements on c-axis films. Films grown on miscut (vicinal) substrates have a reduced measurement symmetry and thus provide a greater insight into the critical current anisotropy. In this paper previous descriptions of the magnetic field angle dependence of j(c) in YBa2Cu3O7-delta are reviewed. Measurements on YBa2Cu3O7-delta thin films grown on a range of vicinal substrates are presented and the results interpreted in terms of the structure and dimensionality of the flux line lattice in YBa2Cu3O7-delta. There is strong evidence for a transition in the structure of the flux line lattice depending on magnetic field magnitude, orientation, and temperature. As a consequence, a simple scaling law cannot, by itself, describe the observed critical current anisotropy in YBa2Cu3O7-delta. The experimentally obtained j(c)(theta) behavior of YBa2Cu3O7-delta is successfully described in terms of a kinked vortex structure for fields applied near parallel to the a-b planes.