Observation of melting of solid He-4 by sound wave

We have observed the crystal melting, or the depletion of the solid/liquid interface where the strong pulsed sound beam was passing. The crystal was p roduced around 0.8 K with the atomically rough horizontal surface sitting i n the middle of the sample cell. The interface was very mobile which was co nfirmed by an easy excitation of the crystallization/melting wave. When the received signal through the interface was monitored as a function of the i nput power, a sudden saturation of the received signal was observed at some power. For well above that power, the melting of the interface was visible through a video camera for both the cases of the sound emission from fluid -side and solid-side. This would be the first observation of sound induced melting of solid He-4. (C) 1999 Elsevier Science B.V. All rights reserved.