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

Abstract

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 deoxygenated YBa2Cu3O7−δ thin films and optimally oxygenated Y0.75Ca0.25Ba2Cu3O7−δ thin films. The films were grown on 10° miscut SrTiO3 substrates to enable the intrinsic vortex channeling effect to be observed. The form of the vortex channeling minimum observed in field angle dependent critical current studies on the films was seen to depend on film oxygenation. The vortex channeling effect is dependent on a angular dependent crossover to a string-pancake flux line lattice. The results obtained appear to be consistent with the prediction of [G. Blatter, M. V. Feigelman, V. B. Geshkenbein, A. I. Larkin, and V. M. Vinokur, Rev. Mod. Phys. 66, 1125 (1994)] that increased superconducting anisotropy leads to the kinked string-pancake lattice existing over a smaller angular range.