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 YBa₂Cu₃O_7-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 Θₒₚₜ0ex0ex=0ex0ex±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.