Superfluid 4He dynamics beyond quasiparticle excitations
K. Beauvois, C. E. Campbell, J. Dawidowski, B. F{\aa}k, H. Godfrin, E., Krotscheck, H.-J. Lauter, T. Lichtenegger, J. Ollivier, A. Sultan
TL;DR
This study investigates superfluid helium-4 dynamics beyond quasiparticle energies using high-precision neutron scattering, revealing complex interactions and validating a dynamic many-body theoretical model up to three times the quasiparticle energy.
Contribution
It provides the first detailed experimental and theoretical analysis of superfluid helium-4 dynamics beyond the quasiparticle regime, including three-phonon processes.
Findings
Observation of structured response above quasiparticle spectrum
Identification of sharp thresholds for phonon interactions
Quantitative agreement between experiment and dynamic many-body theory
Abstract
The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a Dynamic Many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.
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