Crystal-field effects in the intermediate-valence compound YbCu2Si2

Inelastic thermal-neutron scattering is used to study the intermediate-valence system YbCu2Si2. The magnetic scattering in two nonoverlapping ranges of transfer energies, 2 < epsilon < 5 meV and 5 < epsilon < 100 meV, is analyzed under the assumption that the regions influence each other only weakly. As a result, two sets of phenomenological crystal-field parameters are established, and their difference constitutes the experimental error in determining these parameters. A comparison of the fourth-order crystal field with other compounds belonging to the RCu2Si2 series (R stands for a rare-earth element) suggests that in YbCu2Si2 hybridization occurs between f electrons and copper electrons, in contrast to the heavy-fermion system CeCu2Si2, for which it was established earlier that hybridization occurs between f electrons and Si p electrons. (C) 1998 American Institute of Physics.