Angular scaling of critical current measurements on laser-ablated YBa₂Cu₃O_7-δ thin films

Orientation dependent measurements of torque hysteresis loops on high quality laser-ablated YBa₂Cu₃O_7-δ thin films were performed at a temperature of 30 K in magnetic fields up to 7 T. From these measurement we extract the field and orientation dependence of the in-plane critical current density J_s(H,θ), where θ is the angle between the applied external magnetic field H and the plane of the film. Following the scaling arguments of Blatter, Geshkenbein and Larkin based on the anisotropic Ginzburg-Landau theory, we have been able to scale the measured J_s(H, θ) into a form ∫(ε{lunate}(θ)H), where ε{lunate} (θ) = (sin² θ + cos² θ/gg²) ^{1 2} with γ = 3.4±0.3. The obtained value of the anisotropy parameter γ is much smaller than the values reported earlier for single crystals close to T_c.