Four-band extended Hubbard Hamiltonian for the one-dimensional cuprate Sr 2 CuO 3 : Distribution of oxygen holes and its relation to strong intersite Coulomb interaction

We have carried out experimental and theoretical studies of the unoccupied electronic structure of Sr 2CuO3, which can be regarded as the best realization of a one-dimensional model system containing cuprate chains. In the polarization-dependent x-ray absorption spectra, the contributions to the upper Hubbard band from states originating from the two inequivalent oxygen sites are energetically well separated. Theoretical analysis of the measured hole distribution within cluster calculations reveals a markedly enhanced effective nearest-neighbor intersite Coulomb interaction, Vpd;2 to 3 eV, or sizable contributions from next-nearest-neighbor interactions, provided a finite on-site energy difference of the two inequivalent oxygen sites D pp is taken into account. Including next-nearest-neighbor interactions, reasonable agreement can be achieved with recent electron energy-loss spectroscopy data from the same compound. The 2p oxygen orbital analysis of the unoccupied electronic structure of the single-chain cuprate Sr 2CuO3 reveals strong similarities with that of the double chain compound SrCuO2.