Bulk Properties of ³He-⁴He Mixtures

Abstract

In the space available it is impossible to review all aspects of research into bulk properties of helium mixtures, and so I shall omit all reference to the thermodynamics of mixtures, a subject which has been thoroughly explored and is reviewed in the articles by Ebner and Edwards¹ and by Ghozlan and Varoquaux². Another excellent review, but with a more theoretical slant, is that of Baym and Pethick³. Rather, I will concentrate on several new ideas have emerged since these reviews were published. For example: it has become clear that, with the advent of large magnetic fields and new cooling techniques, it is possible to polarise dilute mixtures by brute force methods. This has opened up a whole new field of research on degenerate spin polarised Fermi systems, a topic pioneered by Bashkin and Meyerovich⁴. Another new idea: three phonon decay processes are allowed in ⁴He at low pressures,and these processes affect phonon transport in dilute ³He-⁴He mixtures^5,6. Another new field was opened up by the discovery of spin waves in mixtures⁷. These are the topics which I will concentrate on in this review. The transport properties of dilute mixtures near the lambda line, a fascinating subject, will be dealt with elsewhere in the proceedings by Horst Meyer⁸ and Richard Ferrell⁹.