Crossover between fractal and nonfractal flux penetration in high-temperature superconducting thin films

In this study the role of anisotropy on flux penetration in c-axis epitaxial Tl₂Ba₂CuO₆₊ₓ and YBa₂Cu₃O_7-x films is investigated by magneto-optics. We study thin films of Tl₂Ba₂CuO₆₊ₓ on substrates with vicinal angles of 0^∘{} (well-oriented), 0.5^∘, 2.5^∘, and 4^∘ and YBa₂Cu₃O_7-x films as a function of chain-conduction-induced anisotropy. A crossover from fractal to nonfractal flux penetration is observed with increasing anisotropy. Numerical simulations of anisotropic flux motion are compared with experiment.