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Quantum momentum distribution and kinetic energy in solid 4He.
S O Diallo1, J V Pearce, R T Azuah
1Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716-2570, USA.
Physical Review Letters
|August 25, 2004
Summary
Measurements of neutron scattering reveal that the atomic momentum distribution in solid helium-4 deviates significantly from a Gaussian. This quantum solid exhibits a sharper peak and more low-momentum states than previously assumed.
Area of Science:
- Condensed matter physics
- Quantum fluids
- Neutron scattering
Background:
- Solid helium-4 (4He) is a quantum fluid exhibiting unique properties due to quantum many-body effects.
- Understanding the atomic momentum distribution is crucial for characterizing its quantum nature.
Purpose of the Study:
- To measure the atomic momentum distribution, n(k), in solid 4He at high momentum transfer.
- To compare the experimental n(k) with theoretical models and common assumptions.
Main Methods:
- Neutron scattering experiments were performed on solid 4He at high momentum transfer.
- The solid was maintained near its melting line at a molar volume of 20.87 cm3/mol and a temperature of 1.6 K.
Main Results:
- The atomic momentum distribution n(k) in solid 4He was determined.
- n(k) was found to differ significantly from a Gaussian distribution, being more sharply peaked with greater occupation of low-momentum states.
- The average atomic kinetic energy
was measured as (24.25 ± 0.30) K.
Conclusions:
- The anharmonicity of solid 4He leads to a non-Gaussian momentum distribution.
- Assuming a Gaussian n(k) underestimates the atomic kinetic energy by approximately 10%.