Pressure-induced valence and crystal field shifts in YbCu2Si2 and TmTe by neutron scattering

We present the quasielastic and inelastic neutron scattering of YbCu₂Si₂ and TmTe at high pressure and compare the results to those at ambient pressure performed at the same samples. In both cases we found variations of the quasielastic line width due to a pressure-induced 4f valence shift. The observations are shown to be in a gross quantitative agreement with theory as based on the Anderson model and therefore comply with the common picture of a dynamic 4f valence fluctuation. A measured variation of the crystal field parameters in YbCu₂Si₂ indicates a dominant contribution of the conduction electrons to the crystal field rather than the applicability of the Point Charge Model. As a by-product, very general theoretical expressions are provided for the pressure variation of crystal field parameters.This work is faithfully dedicated to Dieter Wohlleben whose tireless scientific truth and enthusiastic visions of the rules of nature will inspire us all forever.