Experimental Identification of Charge Relaxation Rates in Intermediate-Valence Compounds by Phonon Spectroscopy

The charge relaxation rate ${\Gamma }_c$ of intermediate-valence compounds is identified experimentally by the different behavior of the phonon-mode frequencies for $\hslash \omega >>{\Gamma }_c$ and $\hslash \omega \lesssim {\Gamma }_c$. This classification yields a systematic understanding of the occurrence or absence of phonon anomalies in all intermediate-valence compounds investigated so far. A temperature dependence of ${\Gamma }_c$ could be determined in the case of ${\mathrm{Sm}}_{0.75}$ ${\mathrm{Y}}_{0.25}$S.