Melting of Solid 4He by Ultrasound at 1.2 K

We observed the melting of solid 4 He in superfluid when the sound waves were injected to its rough surface at 1.2 K. Single crystal was grown between two transducers and ultrasound pulses were applied normally to the solid-liquid interface from solid side or liquid side. Amount of melting was on the same order in both cases. We developed surface height measurement system using the sound wave itself and measured the amount of melting by changing the sound power and the number of pulses.