Single- vs. multi-orbital theories of the cuprate superconductors: exact results on finite lattices

We present a comparative exact diagonalization study of single- and three-orbital Hubbard models for cuprate superconductors in their respective strong-coupling limits. For the simplest case of the three-orbital model, our results indicate a close quantitative correspondence with the single-orbital model, both in the groundstate properties and in the low-energy excitation spectra, consistent with the theory of Zhang and Rice.