Soft-x-ray emission spectroscopy study of La2CuO4 and three high-Tc superconductors

Core-Level Spectroscopy in High-Tc Superconductors

A short review is presented on the spectroscopic study of X-ray photoemission (XPS), X-ray absorption (XAS) and X-ray emission (XES) associated with the Cu 2p and O 1s core-levels in high- Tc systems and related materials. Experimental data are analyzed using the single-site impurity Anderson model (and its extension) with Cu 3d orbitals and O 2p valence bands specified by irreducible representations of the D4h symmetry around the Cu atom. By analyzing Cu 2p-XPS, we can get information on the hybridization strength between Cu 3d and O 2p states and the charge transfer energy. In determining the spectral shape of the XPS satellite, it is shown that the interplay between the intraatomic multiplet coupling and the solid-state hybridization plays an essential role. The Cu 2p-XAS, especially its polarization dependence, gives the most direct information on the site and the symmetry of doped holes. Finally, we show the Cu 2p-XES can also be interpreted with the impurity Anderson model in a manner consistent with XPS and XAS.