Dissipation in high-temperature superconductors in a magnetic field

The absence of a Lorentz force dependence on dissipation in the highly anisotropic highly high-temperature superconductor, Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub x}, has been measured over a wide range of current densities in broadened resistive transitions, current-voltage characteristics, magnetoresistances, and critical current densities, J{sub c}. The magnetoresistances are very useful to find out the correct temperature and field dependences of the activation energy. As an alternative to flux motion, we consider a Josephson-coupling model which is consistent with the broadened resistive transitions and the lack of Lorentz-force dependence. We found that the Josephson-coupling model agrees with the temperature dependences of the activation energy and J{sub c} and is better matched to the weak field dependence of J{sub c} than the flux creep model. Possible origins of Josephson junctions in high-quality films and single crystals are discussed. 12 refs., 6 figs