Dynamical correlations in one-dimensional charge-transfer insulators

The single-particle spectral function and the density response of a two band Emery model for CuO chains is calculated for large on-site Cu repulsion U and large on-site energy difference $\Delta .$ For $U\gg U-\Delta \gg t$ the eigenfunctions are products of charge and spin parts, which allows analytical calculation of spectral functions in that limit. For other parameters numerical diagonalization is used. The low-energy hole carriers are shown to be the one-dimensional analogs of the Zhang-Rice singlets. The validity of the one-band model is discussed. The results are relevant to the interpretation of photoemission and electron-energy-loss spectroscopy experiments on ${\mathrm{SrCuO}}_2$ and ${\mathrm{Sr}}_2{\mathrm{CuO}}_3.$