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

Magnetic flux penetration in high-temperature superconductors is affec ted by both anisotropic structure and the presence of flux pinning mec hanisms. An AC inductance technique is described which is sensitive to flux penetration in superconductors as a function of field orientatio n. Results of such measurements for YBa2Cu3O7-x crystals are shown to be sensitive to the amount of flux pinning present in individual cryst als and the direction of the applied field. Twinning planes are shown to be a major source of such pinning in YBa2Cu3O7-x. Possible explanat ions for pinning by this mechanism are considered.