Transport Properties of Bi$_2$Sr$_{2-x}$La$_x$CaCu$_2$O$_{8+\delta}$ Single Crystals Grown by a Floating-Zone Method

摘要

A parent insulator of the Bi-based high-$T_c$ superconductorBi$_2$Sr$_{2-x}$La$_x$CaCu$_2$O$_{8+\delta}$ was successfully grown by atraveling solvent floating zone method. The in-plane resistivity $\rho_{ab}$shows metallic behavior ($d\rho_{ab}/dT >$ 0) near room temperature, althoughthe magnitude of the resistivity is far above the Mott limit for metallicconduction. The Hall mobility of the parent insulator does not so much differfrom that of an optimally doped sample. These results suggest that the systemis not a simple insulator with a well-defined gap, and the hole in the parentinsulator is essentially itinerant, as soon as it is doped.