Angular Dependence of Electric Field vs. Current Density Characteristics in YBa_2Cu_3O_y Superconducting Thin Film with Columnar Defects

The effects of columnar defects on the critical current density (Jc) and electric (E) vs. current density (J) characteristics were investigated for a YBa2Cu3Oy thin film prepared using a pulsed-laser deposition method. The YBa2Cu3Oy thin film was irradiated with 200 MeV Au ions from a direction θ=8.8°off the c-axis. Two peaks in the angular dependence of Jc were observed at the angles of θ=8.8°and θ=90°. These angles correspond to the directions of the columnar defect and intrinsic pinning, respectively. The E-J characteristics at various magnetic field angles can be described by the percolation transition model. The value of pinning parameter m increases at the angles of θ=8.8°and θ=90°. This result indicates that the efficiency of flux pinning is enhanced because fluxoids are effectively pinned by the columnar defects and intrinsic pinning or stacking faults in these directions.