We propose an electronic model for the recently discovered hole doped compound Y2−xCaxBaNiO5. From a multiband Hamiltonian with oxygen and nickel orbitals, a one band model is derived. Holes are described using Zhang-Rice-like S=1/2 states at the nickels propagating on a S=1 spin chain. Using numerical techniques to calculate the dynamical spin structure factor S(q,ω) in a realistic regime of couplings, spectral weight in the Haldane gap is observed in agreement with neutron scattering data. Low energy states with S=3/2 appear in the model. Several predictions are made to test these ideas.
@article{arxiv.cond-mat/9508061,
title = {Spin Dynamics of Hole Doped ${\rm Y_{2-x} Ca_x Ba Ni O_5}$},
author = {E. Dagotto and J. Riera and A. Sandvik and A. Moreo},
journal= {arXiv preprint arXiv:cond-mat/9508061},
year = {2009}
}