Phonon Propagation by Quasidiffusion

Experimental observation of quasidiffusive propagation of a nonequilibrium phonon distribution in ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$: V is reported. Among the features of this propagation mode is the fact that the arrival time of the phonon pulse front varies almost linearly with propagation distance as expected for ballistic transport, even though the time-of-flight spectrum has an extended tail characteristic of diffusive transport.