The role of the condensate in the existence of phonons and rotons

Conference · Wed Dec 01 04:00:00 EST 1993 · Journal of Low Temperature Physics; (United States)

OSTI ID:5464259

Glyde, H R ^[1]

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1. Univ. of Delaware, Newark, DE (United States)

Interpretations of the characteristic phonon-roton excitations in superfluid [sup 4]He are discussed to assess the role of the condensate. In the celebrated Landau, Feynman, Feenberg and subsequent Correlated Basic Function methods, the phonon-roton excitations are interpreted as collective density excitations. This picture, suitably modified at higher Q to take account of the correlated motion of neighbors (backflow), provides the best description of neutron scattering data at low temperature. The condensate does not play an explicit role. In the Field Theory, second quantized formulation of Bogoliubov, Hugenholtz and Pines, Gavoret and Nozieres and the subsequent Dielectric Function formulation, the condensate plays an explicit role. Because of the condensate, both regular density (particle-hole) and single particle excitations contribute to the density response. The regular density (two-particle) and single particle excitations mix as particles scatter into and out of the condensate. This Density-Quasiparticle picture provides a good description of the temperature dependence of neutron scattering data. From this description, the phonon at low Q is interpreted as a joint density/quasiparticle mode strongly coupled via the condensate. At higher Q, the sharp maxon-roton is interpreted as a quasiparticle excitation less strongly coupled into the density. The sharp maxon-roton peak is a unique feature of the condensate and could not be observed in S(Q,[omega]) without a condensate.

• OSTI ID: 5464259
• Report Number(s): CONF-9308208--
• Conference Information: Journal Name: Journal of Low Temperature Physics; (United States) Journal Volume: 93:5-6
• Country of Publication: United States
• Language: English

Related Subjects

665420* -- Superfluidity-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOSE-EINSTEIN CONDENSATION
ENERGY-LEVEL TRANSITIONS
EVEN-EVEN NUCLEI
EXCITATION
HELIUM 4
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
NUCLEI
PHONONS
QUASI PARTICLES
ROTONS
STABLE ISOTOPES
SUPERFLUIDITY