Bounds for the phonon-roton dispersion in superfluid {sup 4}He

Journal Article · Sat Jul 01 04:00:00 EDT 1995 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.52.1236· OSTI ID:76450

Boronat, J; Casulleras, J ^[1]; Dalfovo, F ^[2]; Moroni, S ^[3]; Stringari, S ^[4]

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1. Departament de Fisica i Enginyeria Nuclear, Campus Nord B4-B5, Universitat Politecnica de Catalunya, E-08028 Barcelona (Spain)
2. Istituto Nazionale di Fisica Moleculare, Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Italy)
3. Istituto Nazionale di Fisica della Materia, Laboratorio FORUM, Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy)
4. Istituto Nazionale di Fisica Moleculaire, Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Italy)

The sum-rule approach is used to derive upper bounds for the dispersion law {omega}{sub 0}({ital q}) of the elementary excitations of a Bose superfluid. Bounds are explicitly calculated for the phonon-roton dispersion in superfluid {sup 4}He, both at equilibrium ({rho}=0.021 86 A{sup {minus}3}) and close to freezing ({rho}=0.026 22 A{sup {minus}3}). The bound {omega}{sub 0}({ital q}){le}2{ital S}({ital q}){vert_bar}{chi}({ital q}){vert_bar}{sup {minus}1}, where {ital S}({ital q}) and {chi}({ital q}) are the static structure factor and density response, respectively, is calculated microscopically for several values of the wave vector {ital q}. The results provide a significant improvement with respect to the Feynman approximation {omega}{sub {ital F}}({ital q})={ital q}{sup 2}[2{ital mS}({ital q})]{sup {minus}1}. A further, stronger bound, requiring the additional knowledge of the current correlation function is also investigated. Results for the current correlation function are presented.

• OSTI ID: 76450
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 2 Vol. 52; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
COLLECTIVE EXCITATIONS
CORRELATION FUNCTIONS
DISPERSION RELATIONS
HELIUM 4
PHONONS
ROTONS
STRUCTURE FACTORS
SUM RULES
SUPERFLUIDITY