Phonon-packet propagation through solid-liquid interfaces: resonant effects in the presence of a superlattice

Phonon transmission through a solid-liquid interface is enhanced resonantly when a periodic, elastic multilayer (a superlattice) is inserted at the interface. This happens either at an eigenfrequency () of the vibrational mode localized at a superlattice-liquid interface or at a frequency (ν₀) of the extended vibrational state characteristic of a structure with coupled bilayers. We study the unusual features associated with these resonances by considering the transmission and reflection of rectangular phonon packets (with a peak at a or at ν₀ in the frequency space) by numerical simulations. A significant aspect predicted is the universal double-peak structure of the reflected packet, which we can reproduce well by analytic calculations. Numerical examples are developed for systems consisting of a nanometre-scale GaAs/AlAs superlattice inserted at a GaAs-H₂O interface and a millimetre-scale Al/polymer multilayer inserted at an Al-H₂O interface.