A Theoretical Investigation of Bound Roton Pairs in Superfluid Helium-4 Page: 2
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Cheng, Shih-ta, A Theoretical Investigation of Bound
Roton Pairs in Superfluid Helium-4. Doctor of Philosophy
(Physics), August, 1974, 167 pp., 11 tables, 18 figures,
bibliography, 69 titles.
The Bogoliubov theory of excitations in superfluid helium
is used to study collective modes at zero temperature. A
repulsive delta function shell potential is used in the quasi-
particle excitation energy spectrum to fit the observed
elementary excitation spectrum, except in the plateau region.
The linearized equation of motion method is used to obtain the
secular equation for a collective mode consisting of a linear
combination of one and two free quasiparticles of zero total
momentum. It is shown that in this case for high-lying col-
lective modes, vertices involving three quasiparticles cancel,
and only vertices involving four quasiparticles are important.
A decomposition into various angular momentum states is then
made. Bound roton pairs in the angular momentum D-state
observed in light-scattering experiments exist only for an
attractive coupling between helium atoms in this oversimplified
model. Thus, the interaction between particles can be rein-
terpreted as a phenomenological attractive coupling between
quasiparticles, in order to explain the Raman scattering from
bound roton pairs in superfluid helium.
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Cheng, Shih-ta. A Theoretical Investigation of Bound Roton Pairs in Superfluid Helium-4, dissertation, August 1974; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc501017/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .