Critical Current Density Of Ybco Films With Different Configurations Of Columnar Defects In Longitudinal Magnetic Field

Critical current density (J(c)) properties in longitudinal magnetic fields were investigated for YBa2Cu3Oy thin films with columnar defects (CDs), where different configurations of CDs were systematically installed into the films by using heavy-ion irradiation: a parallel configuration of CDs aligned along the c-axis and two bimodal splay configurations composed of CDs crossing at +/-theta(i) relative to the c-axis, where the splay plane defined by the two irradiation angles is perpendicular or parallel to the transport current direction. The unirradiated film under the longitudinal magnetic field shows a J(c) peak in the magnetic field dependence of J(c), which is 1.1 times higher than the self-field J(c). For the irradiated films with the parallel CD configuration, on the other hand, the J(c) is lower than that for the unirradiated film in all magnetic fields and the value of J(c) decreases with increasing CD density. Such degradation effect by CDs under longitudinal magnetic field was observed even for the bimodal splay configurations. These results are attributed to local meandering of current flow induced by CDs extending through the film thickness, which deteriorates the force-free condition.