Abstract
Due to the peculiar shape of the phonon-roton dispersion curve in 4He, the spontaneous decay of one excitation into a number of others is forbidden for wavenumbers above qc ≃ 0.55 Å−1. Therefore, q > qc excitations can only decay by scattering on another, thermal excitation, and consequently, in the ground state T→ 0 their lifetime becomes infinite, as put to evidence by ballistic photon/roton experimentsl. In contrast the q ≤ qc phonons must have a finite lifetime at T→ 0 and we shall present the first quantitative observation of this phenomenon.
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References
A. F. G. Wyatt, in this volume and references therein.
F. Mezei, The Principle of Neutron Spin Echo, in: “Neutron Spin Echo”, F. Mezei, ed., Springer Verlag Heidelberg (1980).
F. Mezei and W. G. Stirling, Neutron Scattering study of the lifetime of phonons in superfluid 4He, 75th Jubilee Conf. on 4He, J.G.M. Armitage, ed., World Scientific, Singapore (1983).
H.J. Maris, Phonon-phonon interactions in liquid helium, Rev. Mod. Phys. 49: 341 (1977).
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© 1991 Plenum Press, New York
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Mezei, F., Lartigue, C., Farago, B. (1991). Neutron Spin Echo Observation of Spontaneous Phonon Decay in Superfluid 4He. In: Wyatt, A.F.G., Lauter, H.J. (eds) Excitations in Two-Dimensional and Three-Dimensional Quantum Fluids. NATO ASI Series, vol 257. Springer, Boston, MA. https://doi.org/10.1007/978-1-4684-5937-1_10
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DOI: https://doi.org/10.1007/978-1-4684-5937-1_10
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