Conductivity Anisotropy in High T sub c Superconductors

Conductivity measurements in the normal state of single crystal samples of Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 show a remarkable anisotropy of 10 sup 5 between the in-plane and c-axis directions. Critical current measurements show an anisotropy of 10 sup 3 consistent with a Ginzburg-Landau description giving J sup 2 sub ci proportional to rho ni proportional to M sup * sub I. 

The anisotropy can be explained by metallic charge transport within CuO sub 2 planes separated by essentially insulating layers. The charge transport along c is by single particle tunneling in the normal state and by Josephson tunneling in the superconducting state.