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
$B\ \Vert\ ab$
-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.