Temperature Dependence of the Resistivity Tensor in Superconducting ${\mathrm{Bi}}_2$${\mathrm{Sr}}_{2.2}$${\mathrm{Ca}}_{0.8}$ ${\mathrm{Cu}}_2$${\mathrm{O}}_8$ Crystals

A strongly anisotropic resistivity tensor was measured from $T_c=81\mathrm{} \mathrm{to} 600$ K in crystals of the new high-$T_c$ superconductor ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_{2.2}$ ${\mathrm{Ca}}_{0.8}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$. The $a-b$ plane anisotropy is $\frac{{\rho }_a}{{\rho }_b}\approx 2$, with ${\rho }_a$ and ${\rho }_b$ linear in $T$. The perpendicular component ${\rho }_c\sim 10$ Ω cm is ${10}^5$ greater than ${\rho }_a$ or ${\rho }_b$. Evidence for nonmetallic temperature dependence is found for the $\frac{{\rho }_c}{{\rho }_{\mathrm{ab}}}$ resistivity ratio. The data are consistent with the notion of quasiparticle tunneling between planes, but an alternative explanation in terms of weak interplanar coupling by topological defects is also presented.