Extraordinary Electrical Anisotropies in High T sub c Crystals

The three components of the resistivity tensor were measured as a function of temperature in untwinned single crystals of the high-T sub c superconductor having nominal composition Bi sub 2 (Sr, Ca) sub 3 Cu sub 2 O sub 8 (BSCO). In the ab plane an essentially temperature independent anisotropy is found with rho sub a /rho sub b ~ 1.5 - 2.5 from T sub c ~ 81K - 86K up to 600K. The perpendicular component rho sub c is larger than the in-plane components by a factor of about 10 sup 5. The temperature dependence of rho sub c is found to be non-metallic from T sub c to 600K. In the superconducting state a large anisotropic critical current density was measured with J sub (c,ll /J sub (c, ~ 10 sup 2 - 10 sup 3. The measured temperature dependence of the critical current perpendicular to the basal plane J sub (c,) approaches infinity (T sub c - T) is indicative of transport along c via an array of coupled S-N-S junctions acting as weak links between the planes. The dissipation observed at the superconducting transition was found to be caused by excitation of vortex-antivortex pairs within the CuO sub 2 planes and explained quantitatively in terms of the Kosterlitz-Thouless (KT) theory.