Vortex pinning by splayed columnar defects inYBa2Cu3O7:Influence of large crossing angles

Abstract

Various configurations of columnar defects have been installed by heavy-ion irradiation in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ crystals: a standard configuration of tracks parallel to c, a bimodal splay consisting of crossed tracks at $\ifmmode\pm\else\textpm\fi{}5\ifmmode^\circ\else\textdegree\fi{}$ to the c axis, and a ``fan'' configuration consisting of crossed tracks at $\ifmmode\pm\else\textpm\fi{}5\ifmmode^\circ\else\textdegree\fi{}$ and $\ifmmode\pm\else\textpm\fi{}45\ifmmode^\circ\else\textdegree\fi{},$ with a fraction of large angles equal to $1/5.$ The aim is to directly investigate the influence of a small proportion of tracks at large angle on the vortex pinning. This study leads us to conclude that 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.