Slow propagation processes of weak non-equilibrium phonons in mixed crystals

The anomalously slow propagation processes of weak non-equilibrium phonons in a number of mixed crystals are studied experimentally. The dependence of the signal maximum arrival time on temperature, length and composition of a sample is found. It is shown that the observed features of weak non-equilibrium phonon propagation agree satisfactorily with the results of the theoretical calculation in the model involving the intensive Raman phonon-two level system (TLS) coupling in crystals, which results in the energy redistribution between heat pulse and TLS. A possible nature for such TLS in crystals treated is discussed