Enhanced transport properties in YBa₂Cu₃O_x films with crossed columnar defects of various inclination angles

We have studied the effect of heavy-ion irradiation on the transport properties of YBa₂Cu₃O_x thin films. Columnar defects parallel to the c axis (0°) and crossed columnar defects with various inclination angles (θ= ± 10°, ± 20°, and ± 40°) were introduced into films by 1.3 GeV U-ion irradiation with dose equivalent to 1 T vortex density. Transport properties including irreversibility fields, activation energies, and critical current densities have been measured in magnetic fields applied parallel to the c axis. The best transport properties were observed in samples of θ = ± 10° in most of the H-T plane we studied, consistent with the splay model. However, the relative enhancement of the critical current density in the θ= ± 10° compared to the 0° sample was not as large as in the case of a single crystal suggesting that in films the point defects also play an important part in flux pinning.