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Dynamics of liquid 4He in vycor
1Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
Physical Review Letters
|October 4, 2000
Summary
Researchers observed phonon-roton excitations in superfluid helium-4 in Vycor, finding they persist above the superfluid transition temperature. This suggests a separation between Bose-Einstein condensation and superfluidity in confined helium.
Area of Science:
- Condensed matter physics
- Quantum fluids
Background:
- Superfluid helium-4 exhibits unique quantum phenomena.
- Confining helium in porous materials like Vycor can alter its properties.
Purpose of the Study:
- To investigate the behavior of phonon-roton excitations in superfluid helium-4 confined within Vycor.
- To explore the relationship between superfluid fraction and Bose-Einstein condensation in this confined system.
Main Methods:
- Inelastic neutron scattering was employed to probe excitations.
- Measurements were conducted over a wide wave-vector range (0.3–2.15 Å⁻¹).
- Experiments were performed at various temperatures relative to the superfluid transition.
Main Results:
- Well-defined phonon-roton excitations were observed in superfluid 4He within Vycor.
- Excitations showed similar energies and lifetimes to bulk liquid helium-4.
- The intensity of the phonon-roton component did not scale with the superfluid fraction, unlike in bulk helium.
- Phonon-roton excitations persisted above the superfluid transition temperature (Tc = 1.952 K) where the superfluid fraction is zero.
Conclusions:
- The persistence of phonon-roton excitations above Tc in Vycor suggests a decoupling of Bose-Einstein condensation and superfluidity.
- This indicates a potential separation of Bose-Einstein condensation temperature and the superfluid transition temperature in confined helium-4.
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