ANISOTROPY AND FLUX-PINNING IN YBA2CU3O7-X CRYSTALS WITH VARYING TWINNING PLANE DENSITIES

Magnetic flux penetration in high-temperature superconductors is affected by both anisotropic structure and the presence of flux pinning mechanisms. An AC inductance technique is described which is sensitive to flux penetration in superconductors as a function of field orientation. Results of such measurements for YBa2Cu3O7-x crystals are shown to be sensitive to the amount of flux pinning present in individual crystals and the direction of the applied field. Twinning planes are shown to be a major source of such pinning in YBa2Cu3O7-x. Possible explanations for pinning by this mechanism are considered.