Doping dependence of pseudogap and related charge dynamics in Nd_2−xCe_xCuO₄

A notable pseudogap (ΔPG as large as 0.2-0.4 eV) has been found below a characteristic temperature T* in the optical conductivity spectrum for metallic but nonsuperconducting crystals of Nd_2−xCe_xCuO₄(x<0.15). The Δ_PG and T* decrease with doping x, holding the relation of Δ_PG≈10k_BT*. The Drude-like component is observed to evolve concomitantly with the pseudogap. The T* almost coincides with another characteristic temperature T₀ that scales the Hall coefficient. These results indicate that the charge transport in the underdoped region is under the strong influence of the pseudogap state.