NMR in superfluid ³He

Evidence is presented to support the assumption of spin‐triplet p‐wave Cooper pairing in the A and B phases of ³He, and the particular form of the order parameter in each phase follows from available experimental data. Leggett’s description of the spin dynamics shows that the macroscopic condensate qualitatively alters the NMR properties, for the spin density experiences an additional coherent torque that depends on the orientation of the orbital angular momentum of the Cooper pairs. This torque produces many new phenomena, including a temperature‐dependent shift in the transverse CW resonance signal away from the Larmor frequency, resonant absorption in longitudinal CW excitation, and ringing behavior following a sudden perturbation in the applied magnetic field.