Chasing ghosts in reciprocal space—a novel inelastic neutron multiple scattering process

We have discovered that a recently reported weak excitation branch in the spin-Peierls material CuGeO 3 is in fact a ghost image of the primary magnetic excitation shifted in reciprocal space by a novel multiple scattering process. A model is developed that predicts the occurrence of such multiple scattering and accounts for the observations in CuGeO 3. New ‘ghostons’ can occur when the magnetic unit cell is smaller than the structural, while mixing of intensities from different reciprocal space zones jeopardize accurate polarisation analysis and the study of weak modes in general.