Effect of varying material anisotropy on critical current anistropy in vicinal YBa₂Cu₃O₇₋δ thin films

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The high Tc cuprate superconductors are noted for their anisotropic layered structure, certain of these materials indeed tend toward the limit of a Lawrence-Doniach superconductor. However, YBa₂Cu₃O₇₋δ has a smaller anisotropy than would be expected from its interlayer spacing. This is due to the cuprate chains in the structure. To investigate the influence of the chain oxygen on transport properties critical current versus applied field angle measurements were performed on fully oxygenated and de-oxygenated YBa₂Cu₃O₇₋δ thin films and optimally oxygenated Y₀.₇₅Ca₀.₂Ba₂Cu₃O₇₋δ thin films. The films were grown on 10∘ mis-cut SrTiO₃ substrates to enable the intrinsic vortex channelling effect to be observed. The form of the vortex channelling minimum observed in field angle dependent critical current studies on the films was seen to depend on film oxygenation. The vortex channelling effect is dependent on a angular dependent cross-over to a string-pancake flux line lattice. The results obtained appear to be consistent with the prediction of Blatter et al. [Rev. Mod. Phys., 66 (4): 1125 (1994)] that increased superconducting anisotropy leads to the kinked string-pancake lattice existing over a smaller angular range.