Anisotropy of the critical current density in epitaxial YBa2Cu3Ox films

Abstract

The critical current density ${\mathrm{j}}_{\mathrm{c}}$(B,T,θ) of epitaxial, c-axis-oriented ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathrm{x}}$ 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 ${\mathrm{j}}_{\mathrm{c}}$ 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 ${\mathrm{c}}_{66}$, and pinning effects of twin boundaries or stacking faults perpendicular to the film plane, respectively.