Pseudogap phase boundary in overdoped Bi2Sr2CaCu2O8+δ studied by measuring out-of-plane resistivity under the magnetic fields

In order to elucidate the relationship between the pseudogap and high-T c superconductivity, the characteristic pseudogap temperature T* in Bi 2 Sr 2 CaCu 2 O 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 ρ c . Overdoped samples have been prepared by annealing TSFZ-grown Bi 2 Sr 2 CaCu 2 O 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 (= 62 K), while under the magnetic fields of over 3 T, ρ c showed typical upturn behavior from around 65 K upon decreasing temperature. This result suggests that the pseudogap and superconductivity are different phenomena.