Angular variation of pinning near the irreversibility temperature in single crystal YBa2Cu3O7-δ with splayed columnar defects

We have studied vortex pinning through ac susceptibility measurements in single crystals of YBCO with columnar defects (CDs). The CDs have 0 degrees, 10 degrees and 20 degrees splay angle and average direction 10 degrees off the c-axis. By studying the angular variation we can compensate for the anisotropy and effects of twins, etc. Using a simple expression we can obtain the angular spread when the field direction is outside the splay angle. An increase of pinning when the field direction is inside the angle defined by the CDs can be attributed to vortex entanglement due to the splay and the suppression of the sliding of double kinks. (C) 1998 Published by Elsevier Science B.V. All rights reserved.