Pinning and dynamics of magnetic flux in YBaCuO single crystals for vortex motion along twin boundaries

Current-voltage characteristics of YBaCuO single crystals are studied for a Lorentz force aligned along the twin planes. The temperature dependences of the depinning critical currents are determined in magnetic fields that are parallel or tilted with respect to the twin planes for magnetic field vectors oriented almost along axis c. A nearly 50% decrease in the critical current in parallel magnetic fields is attributed to the plastic flow of vortices along channels formed by twin boundaries. It is shown that the resistance to the viscous flux flow is described quite correctly by the Bardeen-Stephen model. The peculiarities in the current and temperature dependences of the differential resistivity at temperatures higher than the melting point but lower than the temperature of onset of vortex pinning by twin boundaries are attributed to the coexistence of solid and liquid vortex phases in this temperature region. A large number of peaks observed in the current dependences of the differential resistivity in a parallel field at temperatures below the melting point of the vortex lattice is associated with nonuniform indirect vortex pinning caused by the fluctuations of the separation between twins. (C) 1997 American Institute of Physics. [S1063-777X(97)00312-5].