Magnetic field dependence of the critical current anisotropy in normal metal-YBa2Cu3O7-δ thin-film bilayers

We have measured the transport critical current density (Jc) in epitaxial quality films of YBa2Cu3O7-δ some of which were covered by thin (10 nm) Ag films. The films, both with and without Ag, had Jc values greater than 106 A/cm2 in liquid nitrogen. The effect of the Ag was to greatly reduce the dependence of Jc on external magnetic fields in the case where the field was oriented in the plane of the film, that is, perpendicular to the c axis. It is unlikely that the effect is simply due to altered surface pinning, although qualitative agreement with critical state models is observed