Pseudogap in Bi₂Sr₂CaCu₂O_8+δ studied by measuring anisotropic susceptibilities and out-of-plane transport

We find in the Bi₂Sr₂CaCu₂O_8+δ system that the characteristic temperatures T*_χ (below which the uniform susceptibilities χ_ab(T) (H ⊥ c) and χ_c(T) (H ‖ c) decrease) and T*_ρc (below which the out-of-plane resistivity ρ_c(T) shows typical upturn) coincidence for all doping levels. We attribute the T dependence of χ’s and ρ_c to the anomalous (pseudogapped) density-of-states (DOS) in high-T_c cuprates. Furthermore, the anisotropy in the T dependence of χ’s is universal, i.e., χ_c ∝ 1.6χ_ab, showing that there is only a single T-dependent component in the χ’s. This implies that the Curie-like behavior (dχ/dT) observed in overdoped samples is also caused by a DOS effect.