Anisotropy of critical current density in c-axis oriented epitaxial YBa2Cu3O7-δ films

The dependence of critical current density Jc on the angle α between the directions of the applied magnetic field H (which was rotated in the c-axis-I plane) and the in-plane current I was measured on a c-axis oriented epitaxial YBa2Cu3O7-δ films at 81 K, with the magnetic field strength up to 6T. Analysis of the experimental results on the basis of the classical scaling law of pinning force shows that there exist simultaneously planar-pinning and volume-pinning mechanisms, and the contribution of volume pinning increases with decreasing α while that of the planar pinning decreases. We propose that the decrease of Lorentz-force-independent critical current density with increasing H for H//I results from the suppression of superconductivity by the magnetic field. The fact that the contribution of volume pinning increases with decreasing α also arises from the suppression of superconductivity in CuO2 plane by the magnetic field.