Gd substitution effect on the normal-state transport properties of Bi 2Sr 2Ca 1− xGd xCu 2O 8+ δ single crystals

Abstract

Doping dependence of the anisotropic resistivity and in-plane thermopower have been systematically studied for Bi 2Sr 2Ca 1− x Gd x Cu 2O 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.