PB0.4BI1.6SR2CACU2O8+X AND OXYGEN STOICHIOMETRY - STRUCTURE, RESISTIVITY, FERMI-SURFACE TOPOLOGY, AND NORMAL-STATE PROPERTIES

Pb0.4Bi1.6Sr2CaCu2O8+x [Bi(Pb)-2212] single-crystal samples were studied using transmission electron microscopy (TEM), ab-plane (ρab) and c-axis (ρc) resistivity, and high-resolution angle-resolved ultraviolet photoemission spectroscopy (ARUPS). TEM reveals that the modulation in the b axis for Pb(0.4)-doped Bi(Pb)-2212 is dominantly of Pb type that is not sensitive to the oxygen content of the system, and the system clearly shows a structure of orthorhombic symmetry. Oxygen-annealed samples exhibit a much lower c-axis resistivity and a resistivity minimum at 80-130 K. He-annealed samples exhibit a much higher c-axis resistivity and dρc/dT<0 behavior below 300 K. The Fermi surface (FS) of oxygen-annealed Bi(Pb)-2212 mapped out by ARUPS has a pocket in the FS around the M̄ point and exhibits orthorhombic symmetry. There are flat, parallel sections of the FS, about 60% of the maximum possible along kx=ky, and about 30% along kx=-ky. The wave vectors connecting the flat sections are about 0.72(π,π) along kx=ky, and about 0.80(π,π) along kx=-ky, rather than (π,π). The symmetry of the near-Fermi-energy dispersing states in the normal state changes between oxygen-annealed and He-annealed samples. © 1995 The American Physical Society.