MODELING THE THERMALIZATION OF NONEQUILIBRIUM PHONON DISTRIBUTIONS INBULK SINGLE-CRYSTALS

Differentiation between types of particle interactions in single cryst als may be achieved by detecting variation in the frequency distributi on of phonons produced Homogeneous superconducting tunnel junctions of a range of materials can be used to probe phonon distributions above different energy thresholds. The apparent decay times of high energy p honons (and consequently the time evolution of non-equilibrium signals ) become significantly altered by the existence of the thermal phonon background. We have developed a model of the behaviour of phonon distr ibutions and studied the way in which initially non-equilibrium distri butions (superimposed on thermal distributions) thermalise. Good agree ment has been observed between our model and the results obtained with superconducting tunnel junctions observing the phonon flux from laser excitations on Nb single crystals.