INFLUENCE OF TWINS ON THE CRITICAL-CURRENT IN YBACUO SINGLE-CRYSTALS

Induction profiles in an inhomogeneously twinned YBa2Cu3O7-delta singl e crystal were measured using a recently developed magneto-optic techn ique. The critical current value J(c) was derived from these profiles and temperature dependences of J(c) for twinned and untwinned regions were built. Twin boundaries are shown to contribute essentially to pin ning at temperatures above 45 K, while at lower temperatures other def ects dominate. A model is suggested which explains the exponential cha racter of J(c)(T) obtained for the untwinned region.