Abstract
Density and spin fluctuations in liquid 3He and 3He- 4He mixtures have been studied by neutron inelastic scattering. We discuss the similarities between the density fluctuations in normal liquid 3He and superfluid 4He (anomalous dispersion and the ‘roton minimum’ that reflects the local order) as well as damping mechanisms that could explain the large width of the 3He zero-sound mode. A line-shape analysis shows that existing theories cannot describe the spin fluctuations observed in liquid 3He. In 3He- 4He mixtures, the shift and broadening of the phonon-roton mode is critically analyzed in terms of Landau damping. The 3He quasiparticle dispersion, and therefore the effective mass, obtained from neutron scattering measurements on 3He- 4He mixtures, shows a clear temperature dependence. Although this is in contrast to what is normally assumed, the specific heat calculated from this dispersion is in excellent agreement with thermodynamic measurements.
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