Pseudogap phase boundary in overdoped Bi_2Sr_2CaCu _2O_(8+δ) studied by measuring out-of-plane resistivity under the magnetic fields

摘要

In order to elucidate the relationship between the pseudogap and high-T_c superconductivity, the characteristic pseudogap temperature T in Bi_2Sr_2CaCu_2O_(8+δ) system has been systematically evaluated as a function of doping, especially focusing on its overdoped region, by measuring the out-of-plane resistivity ρc. Overdoped samples have been prepared by annealing TSFZ-grown Bi_2Sr_2CaCu_2O_(8+δ) single crystals under the high oxygen pressures (990 kgf/cm~2). At a zero field, the ρ_c showed a metallic behavior down to T _c(=62K), while under the magnetic fields of over 3 T, ρc showed typical upturn behavior from around 65 K upon decreasing temperature. This result suggests that the pseudogap and superconductivity are different phenomena.