Abstract
We study the effects of charge degrees of freedom on the spin excitation dynamics in quasi-one-dimensional
magnetic materials. Using the density matrix renormalization group method, we calculate the dynamical spin
structure factor of the Hubbard model at half electronic filling on a chain and on a ladder geometry, and compare
the results with those obtained using the Heisenberg model, where charge degrees of freedom are considered
frozen. For both chains and two-leg ladders, we find that the Hubbard model spectrum qualitatively resembles the
Heisenberg spectrum—with low-energy peaks resembling spinonic excitations—already at intermediate on-site
repulsion as small as U/t ∼ 2–3, although ratios of peak intensities at different momenta continue evolving with
increasing U/t converging only slowly to the Heisenberg limit. We discuss the implications of these results for
neutron scattering experiments and we propose criteria to establish the values of U/t of quasi-one-dimensional
systems described by one-orbital Hubbard models from experimental information.
