Nonlinear acoustic spectroscopy on the real squashing collective mode in ³He-B

We have excited the real squashing (RSQ) collective modes in 3He-B with two simultaneous ultrasound pulses, yielding two-phonon absorption (TPA). We also detected TPA using single-frequency high-intensity sound pulses. The Zeeman splitting of the parametrically excited RSQ mode has been demonstrated. We checked the dispersion relations of the J=2+ modes in zero magnetic field and extracted the collective mode velocities directly from experiments.