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Excitations in the quantum liquid 4He: A review
1Department of Physics and Astronomy, University of Delaware, Newark, DE 19716-2593, United States of America.
Reports on Progress in Physics. Physical Society (Great Britain)
|November 24, 2017
Summary
This review details advances in understanding elementary excitations in superfluid and normal liquid helium-4. It highlights how these excitations, measured by neutron scattering, reveal quantum properties like superfluidity and Bose-Einstein condensation.
Area of Science:
- Condensed matter physics
- Quantum fluids
- Low-temperature physics
Background:
- The study of elementary excitations in liquid helium-4 is crucial for understanding its quantum properties.
- Previous reviews from the early 1990s need updating with recent data and interpretations.
- Superfluidity and Bose-Einstein condensation are key phenomena influenced by these excitations.
Purpose of the Study:
- To provide an updated review of measurements and interpretations of elementary excitations in bulk liquid helium-4.
- To connect the understanding of excitations with superfluidity and fundamental quantum liquid calculations.
- To emphasize the role of Bose-Einstein condensation in the temperature dependence of specific excitation modes.
Main Methods:
- Inelastic neutron scattering is the primary experimental technique discussed.
- Analysis focuses on both collective excitations (phonon-roton modes) and single-particle excitations.
- Theoretical calculations and comparisons with experimental data are integral.
Main Results:
- Advances in measuring and interpreting phonon-roton modes and single-particle excitations are presented.
- The atomic momentum distribution and Bose-Einstein condensate fraction are determined from high-energy excitations.
- The temperature dependence of the [Formula: see text] mode is shown to be significantly influenced by Bose-Einstein condensation.
Conclusions:
- Elementary excitations in liquid helium-4 provide a window into its quantum nature and superfluidity.
- Inelastic neutron scattering remains a powerful tool for probing these excitations.
- Normal liquid helium-4 shares similarities with other quantum and classical liquids, offering broader comparative insights.
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