DAMPING OF INTERFACIAL WAVES IN HE-3-HE-4 LAYERED MIXTURES

The dispersion relation of interfacial waves is calculated for a layer ed almost pure He-3 phase above a He-3-He-4 mixture. Both the real and imaginary parts of the ripplon frequencies are evaluated by taking in to account the essential process of viscous attenuation for various va lues of the He-3-enriched film thickness. We have also considered the van der Waals coupling between the phases. Starting from the spectrum in the case of ideal fluids, the evolution of the spectrum of coupled oscillations of both liquid interfaces is studied by increasing step b y step the liquid-helium viscosity up to its experimental value. We sh owed that ripplon excitations are low damped in a wide range of wave n umbers in contrast to the sound like branch, which is strongly attenua ted due to viscous forces.