Electronic structure of superconducting and non-superconducting Pr ₂Ba₄Cu₇O_15-δ revealed by photoemission spectroscopy

In order to understand the nature of chain-driven superconductivity in Pr₂Ba₄Cu₇O_15-δ (Pr247), we have studied the electronic structure of as-sintered non-superconducting Pr247 and annealed superconducting Pr247 samples using photoemission spectroscopy. The O 1s, Ba 3d, Pr 4d, and Cu 2p core-level energy shifts by annealing indicate that electrons doped by the annealing mainly fill the localized Fehrenbacher-Rice (FR) state. The photoemission spectra ρ(ω) near the Fermi level (E_F) are derived from the metallic Cu-O double chain and can be fitted to the power-law function plus step function Aω ^α + Bθ(ω). ρ(ω) near E_F is indistinguishable between the as-sintered and annealed Pr247 and the exponent α is ∼1.5. These results indicate that the Cu-O double chain provides the spectral weight near E_F and that the annealing affects the localized F_R state instead of the near-EF state.