Direct evidence for an effect of twin boundaries on flux pinning in single-crystalYBa2Cu3O6+x

Magnetization measurements are reported on a nearly cubic single crystal YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} which displays predominantly one variant of twin boundary. With this crystal, we were able to compare the effects of different vortex and twin-boundary orientations on magnetic behavior. The results demonstrate that there is a measurable effect due direct pinning of vortices by twin boundaries for applied fields perpendicular to the {ital c} axis. We also show that the large anisotropy in flux pinning for applied fields parallel and perpendicular to the {ital c} axis is not due to pinning by twin boundaries.