HIDDEN ORDER AND PSEUDOGAP OF Pb-SUBSTITUTED Bi2201 STUDIED BY SCANNING TUNNELING MICROSCOPY AND OUT-OF-PLANE RESISTIVITY IN MAGNETIC FIELDS

We have performed measurements of the out-of-plane resistivity ρ_c in magnetic fields up to 40 T and the scanning tunneling microscopy (STM) in the Pb-Substituted Bi2201. Two kinds of pseudogaps PG1 and PG2 are found at T*₁ and T*₂ below which the nonmetallic ρ_c starts to develop and to be suppressed in magnetic fields with decreasing temperature, respectively. The obtained phase diagram indicates that the pseudogap related to the superconductivity is not PG1 but PG2. STM images of the Bi(Pb)-O plane in the optimally doped sample show bright atom-strings at V ≤ 10 mV. The observed structure may indicate the one-dimensional correlation which is different from the 4a × 4a structure reported in other systems.