The weak center nature and their pinning anisotropy of radiation damage defects in Y1Ba2Cu3O7−δ single crystals

A field induced weak pinning center, in MeV proton irradiated Y₁Ba₂Cu₃O_7−δ (YBCO) single crystal and in ⁶Li-doped sintered YBCO exposed to thermal neutron irradiation, has been identified. The pinning contribution of those radiation caused weak centers (RWCs) showed strong field dependence, which resembles that of the common weak centers of oxygen deficient regions (OWCs) in most of the bulk YBCO materials. The radiation dose dependence of the pinning enhancement, in proton irradiated single crystal, showed strong angular dependence, when the field orientation relative to the crystal was changed. This is believed to be due to the different flux line size (orξ) in different directions, and the so caused volume or line pinning effects. No angular dependence has been observed in neutron irradiated YBCO, which is polycrystalline in nature.