Sound propagation in superfluid ³He B

This review describes sound propagation in the normal state and the superfluid B phase of ³He. The l=1 nature of Cooper pairing in superfluid ³He leads to a complex collective mode spectrum. A number of the collective modes couple to sound. The expressions for the collective mode frequencies are derived using a phenomenological theory. Cryogenic and ultrasonic measurement techniques are briefly discussed, followed by a review of the results of sound propagation experiments, in particular those that show coupling to the collective modes. The effects of fields, textures and dispersion are also reviewed.