MAGNETIC-FIELD, TEMPERATURE, GEOMETRY, AND ANGLE-DEPENDENT STUDIES OFVORTEX PINNING IN VIBRATING HIGH-T(C) SUPERCONDUCTOR CRYSTALS

From the measurement of the resonance frequency and energy dissipation , we have studied the vortex pinning properties of several vibrating h igh-T(c) superconductor crystals YBa2Cu3O7, Bi2Sr2CaCu2O8+x, and oxyge n-reduced Y(6% Gd)Ba2Cu3O6.83. We have studied the response of the cry stals under magnetic field (0 T less-than-or-equal-to B less-than-or-e qual-to 8 T), temperature (10 K less-than-or-equal-to T less-than-or-e qual-to 120 K), angle between field and CuO2 planes (0-degrees less-th an-or-equal-to theta less-than-or-equal-to 90-degrees), and for differ ent geometrical arrangements and driving forces. We can understand the enhancement of the resonance frequency with field taking into account the geometry of the crystals and their orientations. In a certain tem perature and field range our results indicate that ''Josephson vortice s'' in Bi2Sr2CaCu2O8+x remain pinned. At angles 0-degrees < theta < 90 -degrees we have measured double dissipation peaks in all the crystals investigated. This effect can be quantitatively understood with the t hermally activated depinning and vortex diffusion model using resistiv ity data from literature. We discuss briefly unique dissipation featur es measured in Y- and Bi-based superconductors.