In general, elementary excitations like phonons and crystal field (CF) transitions are considered decoupled and the determination and interpretation of the measured spectra of both phenomena, i.e. the phonon dispersion relations and the CF level schemes are made independently of each other. A signature of a strong coupling between both phenomena is the observation of an unusual behaviour in both subsystems. In this paper, we present inelastic neutron scattering results on the rare earth compound CeCu2. This substance shows a orthorhombic CeCu2structure with 18 phonon modes and a splitting of the J = 5/2 ground state multiplet of the Ce3+ions into 3 doublets. The assumption of a coupling between a CF transition connecting the two excited CF states and phonons was put forward from the results of inelastic neutron data on a polycrystalline sample. This assumption is now confirmed by inelastic neutron spectra on a single crystal showing unusual phonon energy shifts and line widths as well as a strong broadening of the CF excitations. © 2003 Elsevier Science B.V. All rights reserved.
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