Excitations and Bose-Einstein condensation in liquid {sup 4}He
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States)
We present a model of the dynamic structure factor S(Q,{omega}) of {sup 4}He that reproduces the basic features of the temperature dependence of S(Q,{omega}) as observed in inelastic-neutron scattering measurements. Wave vectors Q beyond the roton (Q>2.0 A{sup -1}) are considered. The model is able to reproduce the decrease in the intensity of the single excitation (phonon-roton) peak in S(Q,{omega}) with an increase of temperature (T) in the range 0.6{<=}T{<=}2.1 K. All vertices and interactions are assumed temperature independent, and only the condensate fraction n{sub 0}(T) changes with T. Also, it reproduces a second peak observed at higher energy ({omega}) which represents the single excitation intensity lying in the two excitation band. The model is based on the formulation of S(Q,{omega}) of Gavoret and Nozieres. In this formulation, the dynamic susceptibility, {chi}, is separated into a singular part involving the condensate and a regular part involving states above the condensate {chi}={chi}{sub S}+{chi}{sub R}{sup '}. The weight of the phonon-roton peak in {chi}{sub S} is proportional to n{sub 0}(T) and the phonon-roton peak disappears completely from {chi} in the normal phase where n{sub 0}(T)=0. Using sum rule arguments, the condensate fraction can be estimated from the data giving values in good agreement with accurate measurements at SVP and with Monte Carlo calculations.
- OSTI ID:
- 20664917
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 70, Issue 14; Other Information: DOI: 10.1103/PhysRevB.70.144511; (c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOSE-EINSTEIN CONDENSATION
CONDENSATES
EXCITATION
HELIUM 4
INELASTIC SCATTERING
INTERACTIONS
LIQUIDS
MONTE CARLO METHOD
NEUTRON DIFFRACTION
PHONONS
ROTONS
STRUCTURE FACTORS
SUM RULES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0000-0013 K
VECTORS