Pseudogap in Bi2Sr2CaCu2O8+d studied by measuring anisotropic susceptibilities and out-of-plane transport

We find in the Bi2Sr2CaCu2O8+d system that the characteristic temperatures T*_chi [below which the uniform susceptibilities chi_ab(T) (H perpendicular to c) and chi_c(T)(H parallel to c) decrease] and T*_rho_c (below which the out-of-plane resistivity rho_c(T) shows typical upturn) coincide for all doping levels. We attribute the T dependence of chi’s and rho_c to the anomalous (pseudogapped) density-of-states (DOS) in high-Tc cuprates. Furthermore, the anisotropy in the T dependence of chi’s is universal, i.e., chi_c proportional to1.6chi_ab, showing that there is only a single T-dependent component in the chi’s. This implies that the Curie-like behavior (dchi/dT<0) observed in overdoped samples is also caused by a DOS effect.