Spin and orbital dynamics of superfluid ³He

This chapter discusses a combination of hard core repulsive interaction and the strong spin fluctuations that exist in liquid ³He (helium). The dependence of the energy of superfluid ³He on the orientation of the broken symmetry variables is a recurring theme throughout the chapter. These energies are necessarily much smaller than the pairing energy stabilizing the superfluid phase if a description in terms of only the broken symmetry variables is to be valid. Contributions to the energy come from spatial inhomogeneities, the spin–orbit interaction, applied flows and fields, and from the proximity of surfaces. The existence of a “bending energy”—an energy resisting spatial variations of the order parameter—is obvious. Gradients of the order parameter also lead to super currents of both mass and spin.