Large Transport Properties of Bi₂Sr₂₋ₓLaₓCaCu₂O₈₊δ Single Crystals Grown by a Floating-Zone Method

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A parent insulator of the Bi-based high-Tc superconductor Bi₂Sr₂₋ₓLaₓCaCu₂O₈₊δ was successfully grown by a traveling solvent floating zone method. The in-plane resistivity ρab shows metallic behavior (dρab/dT > 0) near room temperature, although the magnitude of the resistivity is far above the Mott limit for metallic conduction. The Hall mobility of the parent insulator does not so much differ from that of an optimally doped sample. These results suggest that the system is not a simple insulator with a well-defined gap, and the hole in the parent insulator is essentially itinerant, as soon as it is doped.