Vortex pinning by splayed columnar defects in YBa2Cu3O7: Influence of large crossing angles

Various configurations of columnar defects have been installed by heavy-ion irradiation in YBa2Cu3O7 crystals: a standard configuration of tracks para llel to c, a bimodal splay consisting of crossed tracks at +/-5 degrees to the c axis, and a "fan" configuration consisting of crossed tracks at +/-5 degrees and +/-45 degrees, with a fraction of large angles equal to 1/5. Th e aim is to directly investigate the influence of a small proportion of tra cks at large angle on the vortex pinning. This study leads us to conclude t hat the large-angle tail of a Gaussian angular distribution should not, in itself, impede the occurrence of a beneficial splay effect, i.e., a further pinning enhancement relative to a standard irradiation along c. [S0163-182 9(99)00113-7].