ANGULAR DEPENDENT TRANSPORT STUDIES IN THE MIXED STATE OF YBA2CU3O7-Y AND BI2SR2CACU2O8+Y

Precise angular dependent transport measurements have been carried out on thin film samples of YBa2Cu3O7-y and Bi2Sr2CaCu2O8+y in their magnetic field induced resistive state. In the epitaxial YBa2Cu3O7-y films, angular dependent resistivity exhibits features associated with the ab-plane anisotropy and also the influence of twin boundaries. Observation of transverse resistivity comparable in size with the longitudinal resistivity gives strong evidence for flux dynamics as the essential mechanism of energy dissipation in the mixed state. Dependence on the relative angle between transport current and magnetic field is observed in YBa2Cu3O7-y particularly clearly in the high current density case and is qualitatively consistent with the Lorentz-force-driven flux motion. This is to be contrasted with the case of Bi2Sr2CaCu2O8+y in which the dissipation is independent of the current direction. A model for the flux dynamics in highly anisotropic layered superconductors is discussed as a possible interpretation of the anomalous Lorentz force independence in the latter system. © 1990.