Probing of carriers in oxide superconductors

We report progress in the electron energy-loss spectroscopy (EELS) study of the high-temperature superconductors, concentrating mainly on the near-edge-structure in the core absorption edges. We can identify the pre-edge peak in the O 1s absorption edge with the hole carrier concentration in the p-type oxide superconductors. With the small probe available in a dedicated scanning transmission electron microscope (STEM), local carrier distribution can be measured. Furthermore, small changes in its oxygen content can be inferred directly from the measured hole density in YBa2Cu3O7-δ. Successful applications of the EELS technique include the characterization of hole concentration in Ca doped YBa2Cu3O7-δ, the determination of oxygen stoichiometry near grain boundaries in YBa2Cu3O7-δ, and the identification of the local electronic structure associated with defects in Bi2Sr2Ca2Cu3O10. (orig.)