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 spl ayed configurations. The largest J is obtained for a planar distributi on P-pl(Theta), with a splay angle Theta(opt) = +/-5 degrees. A compar ison of P-pl(Theta) and a Gaussian distribution P-G(Theta) suggests th at pinning by the latter is controlled by large-angle tails of the Gau ssian which appear to enhance thermal creep rate. Numerical simulation s confirm the existence of the regimes where vortex motion is promoted rather than suppressed by splay.