Transport critical currents and flux pinning mechanisms in single-crystalline thin films of YBa 2Cu 3O 7−δ

Abstract

In order to investigate the anisotropy of transport critical current densities J c and flux pinning properties, we have measured J c for YBa 2Cu 3O 7-δ single-crystalline thin films in magnetic fields H up to 12 T as a function of the angle between H and the crystal axes. The observed angular dependence of J c at 77 K and near 1.0 T could be explained by the model of intrinsic flux pinning proposed by Tachiki and Takahashi under the condition of transport current I ⊥ H . However, in a high field region near the upper critical field H c2, the results disagreed with this model. We found that the reduced field H/ H c2 dependence of the volume pinning force F p could be represented by F p ∝ ( H/ H c2) 1 2 (1- H/ H c2) 2 for all configurations for which we measured. The results indicate that both intrinsic and extrinsic pinning centers worked as a surface-type (two-dimensional) pinning. Furthermore, the angular dependence of H c2 was explained by the effective mass model.