Angular behaviour of critical current density in YBa₂Cu₃O_y thin films with crossed columnar defects

Columnar defects (CDs) were installed into YBa₂Cu₃O_y thin films at the crossing angle ± θ _i relative to the c-axis using 200 MeV Xe ions, in order to clarify the influence of ± θ _i on the angular behaviours of critical current density J _c. The width of a J _c peak occuring at B || c linearly increases with broadening CD-crossing angle, where its shape maintains a single peak in the range of θ _i ≤ ± 25°. The CDs crossing at ± 45°, on the other hand, drastically change the angular behaviour of J _c around B || c: the J _c is equally elevated over the angular region from -45° to 45° in the lower magnetic field, whereas the rapid reduction of the J _c occurs at B || c with increasing magnetic field, leading to the appearance of double peaks near the irradiation angles, ± 45°. This crossover phenomenon is attributed to the difference in the pinned states of flux lines between B || c and at the irradiation angles: the CDs crossing at ± 45° cannot provide the correlated flux pinning along the c-axis, resulting in the uncorrelated pinned state at B || c.