Gd substitution effect on the normal-state transport properties of Bi2Sr2Ca1−xGdxCu2O8+δ single crystals

Doping dependence of the anisotropic resistivity and in-plane thermopower have been systematically studied for Bi 2 Sr 2 Ca 1− x Gd x Cu 2 O 8+ δ single crystals ( x =0, 0.09, 0.19, 0.32 and 0.41), whose hole concentration changes from overdoped to underdoped level. For the underdoped crystals, the in-plane resistivity ρ ab ( T ) exhibits an obvious downturn from the T -linear behavior at characteristic temperature T * , whose value increases with x , which manifests the opening of the spin gap in the normal state. The c -axis resistivity ρ c ( T ) and the anisotropy ρ c ( T )/ ρ ab ( T ) increase rapidly with increasing Gd-doping concentration. The in-plane thermopower S increases monotonously with decreasing the carrier concentration, and its temperature dependence for the underdoped crystals shows a deviation from the T -linear dependence at high temperature region. By assuming a characteristic temperature T scale where the thermopower S begins to deviate from T -linear behavior, S ( T )/ S ( T scale ) vs. T / T scale can be well scaled into a universal curve for all the underdoped crystals. The T scale , which is supposed to relate with pseudogap, shows the similar doping dependence to that of T * . However, there are quantitatively difference between T * and T scale .