Rychtmyer-Meshkov instability and solid ⁴He melting driven by acoustic pulse

Recent experiments have shown remarkable dynamics of solid $^4$He melting and growth, driven by the normal incidence of an acoustic pulse on the solid-liquid interface. The theory of solid growth/melting, driven by the radiation pressure of the acoustic pulse, accounts well for the temperature dependence of the measured data. There is however an observed source of extra, temperature-independent, melting. We here propose that this extra melting is due to solid-liquid mixing (and consequent melting) at the interface, in a process similar to the Richtmyer-Meshkov instability: Initial undulations of the rough interface, grow when accelerated by the acoustic pressure oscillations. This model predicts a temperature-independent extra melting and its dependence on the acoustic power, which is in agreement with the measured data.