Anisotropy of the critical current density in epitaxial YBa2Cu3Ox films

The critical current density jc(B,T,θ) of epitaxial, c-axis-oriented YBa2Cu3Ox films was measured between 4.2 and 77 K in magnetic fields up to 8 T as a function of the field direction θ. Strongly enhanced critical currents are observed when the flux lines are aligned along the CuO planes, but there is also a maximum in jc when the magnetic field is adjusted parallel to the c axis. We relate these effects to an intrinsic pinning between CuO layers, an anisotropy of the shear modulus c66, and pinning effects of twin boundaries or stacking faults perpendicular to the film plane, respectively