Inertia of rough and vicinal surfaces of helium-4 crystals

This paper reports a study of the inertia of rough and vicinal of {sup 4}He crystals. We have measured the transmission coefficient of ultrasonic waves at frequencies 10, 30, 50 and 70 MHz, across the liquid-solid interface. The experiments are carried out at temperatures ranging between 0.4 and 1.0 K for four crystallographic orientations. Two important phenomena are put to evidence for the first time. We have found the first experimental evidence that the inertia of rough surfaces depends on temperature. For vicinal surfaces, we have shown the strong increase of the inertia as the tilt angle decreases. Our experimental results agree very well with the theoretical predictions.