Superconductivity and electronic structure of Bi-based compounds

Abstract

We have prepared superconducting Bi-based compounds by sintering and find a weak diamagnetic response at 110 K and a strong diamagnetic response at about 80 K. The dominant structural phase was identified by x-ray diffraction to be ${\mathrm{Bi}}_{2}$${\mathrm{SrCa}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8\mathrm{\ensuremath{-}}\mathrm{y}}$ and low-field magnetization indicates that approximately 60% (by volume) of the sample is superconducting. X\ensuremath{\alpha} and other calculations to interpret the copper binding energies and satellite features of high-${T}_{c}$ superconductors are presented, and these calculations suggest that while x-ray photoemission spectroscopy (XPS) can distinguish between Cu i and Cu ii, it may not be able to unambiguously identify Cu iii. We also find that copper reduction during the XPS experiment further complicates copper oxidation state determination.