Propagation of heat pulses in disordered media

Processes of heat pulse propagation in nonconducting disordered systems containing thermal-phonon trapping centers (two-level systems) are investigated at low temperatures. The main parameters of the model studied, containing two different two-level systems, are the heat capacity of each of the subsystems and the relaxation time for the inelastic scattering of phonons on the two-level systems. The influence of the interaction of phonons with the two-level centers on the time of arrival of the heat pulse at the bolometer is calculated for different densities of centers. The theoretical calculations are compared with the experimental data on the propagation of slightly nonequilibrium phonons in solid solutions of rare-earth yttrium-aluminum garnets and in two-phase ceramics at helium temperatures. (C) 2003 American Institute of Physics.