Pinning mechanism of vortices at antiphase boundaries in YBa2Cu3O7-delta

Using quantitative magneto-optics and inversion of Biot-Savart's law for de termining critical current density distributions, we investigated the aniso tropic vortex pinning at planar defects in YBa2Cu3O7-delta films. Parallel oriented planar antiphase boundaries (APB's) generated in epitaxial thin fi lms grown on vicinal SrTiO3 (001), serve as well defined pinning sites. Thi s array of APB's exerts anisotropic pinning forces on vortex lines which ar e extraordinary high transverse to the boundary yielding a longitudinal cri tical current density j(c,L) up to approximate to 30% of the depairing curr ent parallel to the APB's. Remarkably, also the transverse j(c,T) crossing the APB's is large for smooth and sharp interfaces corresponding to values usually observed in films on well oriented single-crystalline substrates. D ue to variations in the structural width of APB's the magnetic flux penetra ting parallel to the defect plane exhibits a filamentary pattern at low fie lds. It is related to an anomalous low-field dependence of j(c,T) with a ma ximum at approximate to 200 mT. In order to distinguish different pinning m echanisms of vortices at planar defects, the angular dependence of the pinn ing force is calculated approximately and is compared with the experiment. The measured angular and temperature dependence as well as the magnitude of j(c,L). and j(c,T) prove that pinning at APB's is dominated by quasipartic le scattering induced variation of condensation energy, characteristic of s uperconductors with anisotropic order parameter.