Comparison of the CF-induced phonon shifts in CeCu2 and NdCu2

Abstract Elementary excitations in solids like phonons and crystal field (CF) transitions are usually considered to be decoupled. It will be shown that this assumption is only valid in zeroth order. Experimental data, obtained from inelastic neutron scattering, as well as a theoretical model in first-order Taylor expansion will be presented to show a clear evidence of an interaction of the CF-levels and the phonons in the RCu 2 series.