Spin dynamics of hole doped Y2BaNiO5

Abstract

Starting from a multiband Hamiltonian containing the relevant Ni and O orbitals, we derive an effective Hamiltonian $H_{eff}$ for the low energy physics of doped Y${}_2$BaNiO${}_5.$ For hole doping, $H_{eff}$ describes O fermions interacting with S=1 Ni spins in a chain, and cannot be further reduced to a simple one-band model. Using numerical techniques, we obtain a dynamical spin structure factor with weight inside the Haldane gap. The nature of these low-energy excitations is identified and the emerging physical picture is consistent with most of the experimental information in Y% ${}_{2-x}$Ca${}_x$BaNiO${}_5$

4 pages, 2 figures

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