Observation of dispersion in the J=2+ collective modes of B3 by nonlinear acoustic spectroscopy

Parametric excitation yields new results, which cannot be obtained by conventional linear spectroscopy, on the collective modes in superfluid B3. In our ultrasonic experiments, performed in a chamber with four quartz crystals, we have excited the real squashing (J=2+) modes by two simultaneous sound waves which are mutually either parallel, orthogonal, or antiparallel. Qualitatively these results are in agreement with the theoretical dispersion relation of the J=2+ modes, and quantitatively we have been able to extract the collective-mode velocities from the line splittings in zero magnetic field.