Landau model for films and interfaces of superfluid 4HE at T=OK
Ji, Guangda
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https://hdl.handle.net/2142/25229
Description
Title
Landau model for films and interfaces of superfluid 4HE at T=OK
Author(s)
Ji, Guangda
Issue Date
1986
Doctoral Committee Chair(s)
Wortis, M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Landau model
superfluid 4He
free-energy
zero kelvin
Language
en
Abstract
We use a Landau theory appropriate to an inhomogeneous superfluid at
temperature T = 0 to describe structural and dynamical effects at a
gas/superfluid interface and for a superfluid film on an inert attractive
substrate. The parameters of the theory are determined phenomenologically
by fitting measured bulk properties of the homogeneous superfluid. The
theory then predicts in a consistent way both static properties (density
profile, interface/surface tension) and excitations (ripplons, phonons, and
their associated wavefunctions). The simplicity of the theory makes the
connection between the symmetries of the system and the form of the
excitation spectra particularly transparent. In Chapter II, we take the
Landau free-energy functional to be local. This restriction precludes
description of rotan effects. Numerical results are, as a consequence, not
quantitative; however, calculations are easy enough so that generic features
of the spectra and wavefunctions can be illustrated conveniently.
In Chapter III, we allow nonlocality in the free-energy functional, making
it possible to incorporate rotan effects. Two solid-like near-substrate
layers then appear in the film profiles, followed by liquid. The surface
tension obtained is more realistic than that of the local model. A surface
excitation spectrum with a raton-like minimum has been obtained for both a
gas/liquid interface and a film on a graphite substrate. The third-sound
velocities c3 vs. ~P show oscillations characteristic of the layer
structure, which are consistent with measured data if a proper substrate
potential is chosen. A possible form of the effective van der Waals
potential of a graphite substrate, which can explain most experimental
observations, is suggested.
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