Chapter 3 Sound Propagation and Kinetic Coefficients in Superfluid 3He

Abstract

Publisher Summary This chapter reviews the theories of sound propagation and of a number of transport phenomena in the superfluid phases of 3He (helium). The ultrasound propagation have played an important role in identifying the nature of correlations in the ordered phases of liquid 3He, complementing and corroborating the information obtained in NMR (nuclear magnetic resonance) experiments. The measurements of ultrasound absorption in 3He-A and 3He-B have revealed the existence of a new type of collective modes, never observed in nature before, which is closely associated with the tensor as opposed to scalar or vector character of the order. Both sound propagation and transport properties are of interest in that they provide information on the energy spectrum of elementary excitations and their interaction, probing in particular anisotropic properties. Systematic measurements of sound propagation as a function of temperature, pressure, and frequency may be used to determine (1) the gap parameter as a function of temperature and pressure, (2) the quasi-particle lifetime on the Fermi surface in the normal state as a function of pressure, (3) the collision integral parameter , as a function of pressure, (4) the collective mode structure in the A- and B-phases and, thereby the symmetry of these states.