TRANSMISSION OF SOUND AT THE LIQUID-SOLID INTERFACE OF HELIUM - A NEW PROBE OF MELTING KINETICS

An incoming acoustic wave produces an ac discontinuity of chemical potential, DELTA mu at a liquid-solid interface. If melting is fast enough, it responds to such an excitation. It is shown that in quantum systems, in which heat can be evacuated via convection, such an ac melting does occur. It may give rise to a spectacular decrease in sound transmission, and to a conversion mechanism from first to second sound. This effect is analyzed proposing an experiment that should give access to the kinetics of melting when it is too fast to be observed by dc methods.