Enhanced 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−Δ with columnar defects arranged in a variety of splayed configurations. The largest J is obtained for a planar distribution Ppl(Θ), with a splay angle Θopt =+/−5°. A comparison of Ppl(Θ) and a Gaussian distribution PG(Θ) 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. © 1996 The American Physical Society.