2ND SOUNDS IN PHASE-SEPARATING HE-3-HE-4 MIXTURES

Second-sound propagation is investigated in superfluid phases of He-3-He-4 mixtures in the presence of finely divided nonsuperfluid droplets. The attenuation is enhanced by diffusion of the entropy and the He-3 component through the interface. At relatively high frequencies, it is proportional to the surface area density. At very low frequencies, we predict anomalous damping due to first-order phase transition periodically taking place at the interface. The second-sound speed is considerably decreased at low frequencies.