Large pinning efficiency of orthogonal columnar defects in a weakly anisotropic high-Tcsuperconductor

Abstract

The pinning efficiency of orthogonal columnar defects has been investigated in weakly anisotropic ${\mathrm{Tl}}_{2/3}{\mathrm{Bi}}_{1/3}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{7}$ single crystals [denoted as (Tl, Bi)-1212 hereafter]. Columnar defects were introduced by heavy ion irradiation along two directions tilted by 45\ifmmode^\circ\else\textdegree\fi{} from the c axis. This configuration was compared to a crystal irradiated along the c axis. The whole damaged volume was the same in both samples. Magnetic measurements, performed with $\mathbf{H}\ensuremath{\parallel}\mathbf{c},$ show that the perpendicularly crossed defects exhibit the highest pinning efficiency in a wide range of fields and temperatures. To analyze this enhancement, which can be related to the splay of crossed defects and/or to the enlargement of the defect section in the (a,b) planes associated with the tilt angle, the (Tl, Bi)-1212 single crystals were compared to a third one, irradiated along one direction only, tilted by 45\ifmmode^\circ\else\textdegree\fi{} from the c axis. Furthermore, these crystals have been compared to a similar set of defect configurations in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7},$ for a tilt angle of 10\ifmmode^\circ\else\textdegree\fi{}, for which a splay effect has already been demonstrated.