Doping dependence of normal-state transport properties in La- and Pb-doped Bi2Sr2CuOy.

Abstract

We report measurements of the electrical resistivity, thermoelectric power, and Hall coefficient on La- and Pb-doped ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CuO}}_{\mathit{y}}$ compounds as a function of temperature. Both insulating and overdoped nonsuperconducting-metal samples have been obtained. Analysis of the electrical resistivity in the insulating region suggests that the conduction is governed by a variable-range-hopping mechanism in the low-temperature region. As the system changes from a superconductor to an overdoped nonsuperconducting-metal, the resistivity undergoes a change from a linear temperature dependence to a power-law temperature dependence with exponent n\ensuremath{\sim}1.5. This n\ensuremath{\sim}1.5 behavior occurs over a wide temperature range. Remarkable changes associated with the insulator--superconductor-- nonsuperconducting-metal transition are also observed both in the thermoelectric power and the Hall coefficient. A significant difference is that the thermoelectric power becomes negative at the higher doping level, while the Hall coefficient remains positive. We explain the experimental results from a two-carrier model by assuming that the Cu 3${\mathit{d}}_{\mathit{x}}^{2}$-${\mathit{y}}^{2}$ electrons undergo a change from a localized state to a partially delocalized state with an increase in the number of dopant O 2p holes.