One-electron excitations and shake up satellites in Cu K-edge X-ray absorption near edge structure (XANES) of La 2CuO 4 by full multiple scattering analysis in real space

Abstract

The polarized Cu K-edge X-ray Absorption Near Edge Structure (XANES) of La 2CuO 4 has been interpreted by the multiple scattering approach. The size of the cluster of neighbouring atoms having good agreement with the XANES experimental data is determined by 45 atoms surrounding the absorbing Cu. The polarized spectra can be predicted in term of a one-electron dipole (Δ l=+1) transition Cu 1s→ϵp, probing the unoccupied p-like ( l=1) density of states projected on a Cu site with orbital angular momentum ml=0 in the E ∥ z spectra, and the ml=1 for the E ⊤ c spectra. Thus we show that the electronic structure of the high energy conduction bands, beyond the Cu 3d band, of La 2CuO 4 are well described in terms of the one-electron approximation. It is shown that XANES spectra are consistent with the contraction of the Cu-apex oxygen distance with doping. Final state effects induced by the core hole have been indentified: (i) the core transitions take place in the fully relaxed potential, (ii) the satellite at 7 eV above the main K-XANES peak in both polarizations is assigned to a multielectron shake up excitation. Finally the shoulder on the rising absorption edge, present in many Cu compounds and usually assigned to a shake down multi-electron excitation, is shown to be due to a one-electron transition to a state delocalized over a large cluster.