Recent High-Resolution Neutron Scattering Studies of Liquid 4He
Neutron scattering has provided much detailed quantitative information on the nature of the elementary excitations of liquid helium and on the interactions between those excitations. It could reasonably be argued that the most significant features of the excitation spectrum of superfluid 4He were known by about 1975, following the classic investigations of Cowley and Woods 1,2 at Chalk River, and of the Brookhaven group 3,4. The phonon-maxon-roton dispersion curve shown in Fig. 1 had been studied as a function of both temperature and pressure (or equivalently, of density), while the existence of the multiphonon continuum at higher energies had been noted and its relative strength investigated. Nevertheless, neutron scattering studies have continued up to the present day, particularly at Chalk River Nuclear Laboratories and at the Institut Laue-Langevin (I.L.L.). What then was the aim of these second-generation experiments? In their excellent and comprehensive review of neutron scattering studies of solid and liquid helium, published in 1987, Glyde and Svensson5 identified several important questions which remained unanswered in the early 1970s. These ranged from uncertainties as to the form of the dispersion relation at small wavevectors to the origin of the oscillations in the peak position and width of the scattering function S(Q, ω) at large wavevector Q and frequency ω. In addition, the relationship, if any, of the unique excitation spectrum to the existence of superfluidity below Tλ remained a question of profound importance.
KeywordsDispersion Curve Anomalous Dispersion Instrumental Resolution Phonon Peak Neutron Scattering Study
Unable to display preview. Download preview PDF.
- 5.H.R. Glyde and E.C. Svensson, Solid and Liquid Helium, in “Methods of Experimental Physics, Vol 23B; Neutron Scattering”, D.L. Price and K. Sköld, eds., Academic Press Inc. (1987).Google Scholar
- 6.W.G. Stirling, in: “75th Jubilee Conference on Helium-4”, J.G.M. Armitage, ed., p109, World Scientific, Singapore (1983).Google Scholar
- 7.W.G. Stirling, Proc. Int. Conf. Phonon Phys. 2nd, J. Koller, N. Krod, N. Menyhârd and T. Siklós, eds., p. 829, World Scientific, Singapore (1985).Google Scholar
- 8.W.G. Stirling, Proceedings of LT19, Brighton, U.K., August 1990: to be published.Google Scholar
- 11.L.K.H. Andersen, W.G. Stirling, R. Scherm, A. Stunault, B. Fâk, A.J. Dianoux and H. Godfrin, to be published.Google Scholar
- 15.W.G. Stirling, J.R.D. Copley, and P.A. Hilton, in: “Neutron Inelastic Scattering 1977”, Vol. II, p. 45, IAEA, Vienna, (1978).Google Scholar
- 26.L.D. Landau and I.M. Khalatnikov, Zh. Eksp. Teor. Fiz. 19: 637 (1949).Google Scholar
- 27.F. Mezei and W.G. Stirling, in: “75th Jubilee Conference on Helium-4”, J.G.M. Armitage, ed., p111, World Scientific, Singapore (1983).Google Scholar
- 28.H.R. Glyde and A. Griffin, to be published; and this conference.Google Scholar