OBSERVATION OF A 3-DIMENSIONAL VORTEX-LINE LIQUID IN A HIGHLY C-AXIS-ORIENTED (BI,PB)(2)SR2CA2CU3OX SILVER-SHEATHED TAPE

We have measured the temperature dependence of resistance of a highly c-axis-oriented (Bi,Pb)(2)Sr2Ca2Cu3Ox silver-sheathed tape in the mixe d state using the de flux transformer geometry. In the vortex fluid re gime, we have observed the onset of a nonlocal conductivity which corr esponds to the peak (T-peak) in R(bot)(T) curves. This can be explaine d qualitatively in terms of the vortex decoupling which arises from an increased thermal fluctuation. At T < T-peak, the vortices are three dimensional (3D) in character. This behavior is quite different from t he results obtained recently by Safar et al. [Phys. Rev. Lett. 69, 824 (1992)] and Busch et al. [Phys. Rev. Lett. 69, 522 (1992)] in Bi2Sr2C aCu2Oy, single crystals using the same measuring method. Their results show that the vortices are two dimensional in character. The differen ce of the vortex dimensionality between (Bi,Pb)(2)Sr2Ca2Cu3Ox and Bi2S r2CaCu2Oy superconductors in the vortex liquid regime may be attribute d to different anisotropies due to their different crystal structures and pinning disorders. In a 3D vortex line liquid, the results reveal that dissipation seems to originate from the thermally activated plast ic motion of a pinned vortex line liquid. The field and temperature de pendence of the activation energy is as follows: U(H,T) = U-0(1-T/T-c) H--0.45.