Effect of anomalously high oscillations of velocity of longitudinal ultrasound in high pure type I superconductor at weak external magnetic field

We have experimentally observed, for the first time, the very strong oscillations of the velocity of the longitudinal ultrasound attenuation in a normal metal state of the high pure type I superconductor at the magnetic field H at the low temperature of 0.4 K. The oscillations appear, following the change of either: the magnitude of the magnetic field H or the orientation of the magnetic field H in the plane: the magnetic field H perpendicular to the wave vector k.