Charge ordering and spin dynamics in NaV2O5

We report high-resolution neutron inelastic scattering experiments on the s pin excitations of NaV2O5. Below T,, two branches with distinct energy gaps are identified. From the dispersion and intensity of the spin excitation m odes, we deduce the precise zigzag charge distribution on the ladder rungs and the corresponding charge order: Delta (c) approximate to 0.6. We argue that the spin gaps observed in the low-T phase of this compound are primari ly due to the charge transfer.