Electronic Structure and Symmetry of the Itinerant States in High Tc Superconductors

Abstract

The linearly polarized Cu L3 XANES (X-ray Absorption Near Edge Structure) spectra of several high Tc superconductor single crystals and of their parent insulating compounds have been measured. The spectra have been interpreted in the frame of the full multiple scattering (MS) theory in the real space. Over a range of 40 eV, the polarized Cu L3 XANES spectra have been predicted in term of a one-electron dipole (Δl=+1) transitions, probing the partial density of states of the conduction bands projected on the Cu site with the selected orbital angular momentum l=2 and their projections ml. The oscillator strenght for the dipole allowed transitions Δl=-1 has been found to be a factor 100 weaker than the Cu 2p to 3d transitions. The physical origin of all features in the continuum XANES spectra and the effect of the electron-hole Coulomb interaction in the final states have been identified. The difference spectra between the metal and the insulating phase allows to identify the symmetry of the itinerant 3d9L states induced by doping, that is deduced to be a mixture of Cu 3d holes with ml=0, and 2 orbital angular momentum and oxygen 2p holes on planar oxygen in the molecular orbital combination of local a1 and b1 symmetry. Evidence for the more delocalized character of (3d9x2-y2) L(b1) states versus the more localized character of (3d3z2-r2) L(a1) states has been found.