The dependence of the critical current density $j_c$ on the orientation of the magnetic field $\mathbf{H}$ has been measured for a ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ bicrystal film. When the field is rotated in the plane of the grain boundary, $j_c$ displays a maximum for $\mathbf{H}$ close to the $c$ axis in fields up to 7 tesla. The same experiment performed in the interior of the grain shows no maximum. The pinning force at the maximum varies as $H^{0.5}$, consistent with vortex pinning by a dense planar distribution of line pins. These results are a clear demonstration of flux pinning by dislocations in low-angle grain boundaries.

• Received 27 October 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.3855