Theory of X-ray absorption spectra of strongly correlated copper oxides

It has been shown that theoretical X-ray absorption spectra of highly correlated systems can be presented as a product of a single-electron part obtained by the self-consistent field X_α-scattered wave (SCF X_α-SW) method, and of a multi-electron part obtained by exact diagonalization of the Hamiltonian of the multi-band multi-electron p-d model. Using that model, the influence of strong correlation effects on the Cu K- and CuL_2,3-spectra of La_2-xSr_xCuO₄ (x = 0, 0.2, 1) has been studied. In terms of that model, the main peak of the Cu K-spectrum for x = 0 was assigned to the Cud¹⁰L-configuration and only one satellite was assigned to the Cud₉-configuration. Comparison of the theoretical with the experimental data shows that the ground state of the two-holes in the CuO₄ cell is triplet. In that case additional satellites of Cud⁹L- and Cud⁸-configurations are observed. The same conclusions have been made concerning polarized CuL_2,3-spectra for the fully doped LaSrCuO₄ excluding the peak with the energy 2.8 eV above the threshold, which was assigned to the transitions into quasi-stationary states due to existence of a high barrier in the Cud-state Hartree-Fock potential.