Bound State between a Crystal-Field Excitation and a Phonon in CeAl2

Abstract
The existence of a bound state between a crystal-field excitation and a low-lying phonon in CeAl2 is suggested. It can explain in a natural way the hitherto unexplained two-peak structure found in magnetic neutron-scattering experiments. Various checks are made to substantiate this suggestion. A similarity is pointed out to the exciton-phonon bound-state problem in semiconductors.