PREDICTION OF THE TEMPERATURE-DEPENDENT STATIC FORM FACTOR IN HEI AND HE II

A method is presented for predicting the temperature-dependent properties of the static form factor in HeI and HeII at low momenta. The prediction is based upon the observation that a single coherent, collective mode of excitation predominates for temperatures theta < or = 2.57K and momenta k app...

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Bibliographic Details
Main Author: Etters,Richard D
Format: Report
Language:English
Subjects:
BOSONS
EXCITATION
HELIUM
INELASTIC SCATTERING
MATHEMATICAL PREDICTION
MOMENTUM
QUANTUM STATISTICS
Quantum Theory and Relativity
ROTONS
SUPERFLUIDITY
TEMPERATURE
Thermodynamics
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Summary:A method is presented for predicting the temperature-dependent properties of the static form factor in HeI and HeII at low momenta. The prediction is based upon the observation that a single coherent, collective mode of excitation predominates for temperatures theta < or = 2.57K and momenta k approx = 1/0.6A. An expression is developed for the dissipative part of the density-density response function CHI''(k, omega) in the collisionless regime. This result exhibits a slight temperature-dependent energy shift in the position of the main resonance from its value at theta = 0K. However, the 'sharp resonance' structure is retained, reflecting the fact that the collective mode, which is the principal contributor to CHI''(k omega) in the regime considered, exists as a nearly independent mode of excitation for all temperatures theta < or = 2.57K. The expressions for the dynamic and static form factors are derived. They appear to be insensitive to superfluid behavior. The temperature dependence of the static form factor Sk(theta) for 0 < or = theta < or = 2.57K is summarized by the inequalities delta-Sk/delta-theta > 0 for k < 1/0.38A and delta-Sk/delta-theta < 0 for k > 1/0.38A. (Author)