Collective Modes and Nonlinear Acoustics in Superfluid 3He-B

Understand

We discuss the relationship of collisionless sound propagation and attenuation to the order parameter collective modes of superfluid 3He-B.

• These modes, which reflect the symmetries of the normal state as well as the broken gauge and relative rotational symmetries of the condensate, play a central role in the high-frequency acoustic response of the superfluid.
• We review the theory of acoustic spectroscopy based on the linear coupling of the J=2+/- modes.
• We develop the theory of the nonlinear acoustic response of superfluid 3He-B for the case of a three-wave resonance between two sound waves of different frequencies and the J=2+/- modes, as well as the generation of higher harmonic sound waves.