Pinning with controlled splay configurations of columnar defects; rapid vortex motion at large angles

Orders-of-magnitude enhancements of persistent currents J are reported in YBa2Cu3O7-delta with columnar defects arranged in a variety of splayed configurations. The largest J is obtained for a planar distribution P-pl(Theta), with a splay angle Theta(opt) = +/-5 degrees. A comparison of P-pl(Theta) and a Gaussian distribution P-G(Theta) suggests that pinning by the latter is controlled by large-angle tails of the Gaussian which appear to enhance thermal creep rate. Numerical simulations confirm the existence of the regimes where vortex motion is promoted rather than suppressed by splay.