Incommensurate structure factor in a hole-doped spin-1 system

The nickelate compound Y_{2}BaNiO_{5} is a spin-1 Haldane-gap antiferromagnet. The compound is doped with holes on replacing the off-chain Y^{3+} ions by Ca^{2+} ions. Inelastic neutron scattering (INS) experiments reveal the existence of sub-gap states on doping. A recent INS experiment provides evidence for an incommensurate double-peaked structure factor S(q) corresponding to the sub-gap states. In this paper, we formulate a microscopic theory for the origin of the incommensurate peak.