Angular Dependence of Critical Current Density in YBCO Films With Columnar Defects Crossing at Widespread Angles

To investigate whether one-dimensional pinning centers can attain the isotropic critical current density $(J_{\rm c})$ properties, columnar defects (CDs) crossing at widespread angles were installed by heavy-ion irradiation into YBCO thin films. For the sample containing the CDs crossing at 0 $^{\circ}$ , $\pm 30^{\circ}$ , and $\pm 60^{\circ}$ relative to the $c$ -axis, the plateau-like behavior of $J_{\rm c}$ is realized over a wide range of magnetic field orientations, except for around $B \Vert ab$ -plane where a dip structure is accompanied by a rapid decline of the $J_{\rm c}$ . For the bimodal splay configuration consisting of CDs crossing at $\pm 30^{ \circ}$ relative to the $c$ -axis, a single peak around the $c$ -axis is observed in the angular denpendece of $J_{\rm c}$ , suggesting the splay effect at $B \Vert c$ -axis by the crossed CDs. Two parallel families of CDs crossing at $\pm 30^{\circ}$ relative to the $ab$ -plane, on the other hand, bring about not a peak but a dip around -plane on the angular dependence of $J_{\rm c}$ . Apparently, the bimodal splay in CD directions relative to the $ab$ -plane does not contribute to the flux pinning around $B \Vert ab$ -plane, let alone show the splay effect.