Anomaly in the density of phonon states of Tm0.05Y0.95Se

It is well known that phonon anomalies will occur, if the charge relaxation rate is of the same order of magnitude as the phonon frequencies. Such an effect was observed by a strong softening of the LA-mode in <1,1,1>-direction in several intermediate valent systems with NaCl-structure. Here we will report on such an effect, which is found for the first time in a diluted intermediate valent system. We have performed an inelastic neutron scattering experiment on polycrystalline Tm_0.05Y_0.95Se using a time-of-flight spectrometer with a very good energy resolution. As a result of a |Q|-dependent analysis of the measured density of phonon states we found that the LA-mode in <1,1,1>-direction is also strongly softened in this dilute case.