Landau model for superfluid films and interfaces at<i>T=0</i>: Local interactions

Guang-Da, Ji; Wortis, Michael

doi:10.1103/physrevb.34.7704

Cited by 28 publications

(16 citation statements)

References 36 publications

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“…This subject has been reinvestigated recently [4,5] by theorists interested in the properties of inhomogeneous quantum many-body systems. Detailed calculations for the free surface of bulk 4 He, and for films of atomic thickness adsorbed on a solid substrate, at selected coverages, have yielded the dispersion relation and the dynamic structure factor of the elementary excitations in the microscopic regime, i.e., for large wave vectors.…”

Section: Ripplons In 4 He Films Observed By Neutron Scatteringmentioning

confidence: 99%

“…To estimate the total thickness of the film we use for the liquid layers the density of bulk liquid 4 He, obtaining somewhat arbitrarily 0.078 atom/A 2 for the mean density of a liquid layer. This value has to be taken with care, since microscopic calculations show that the density at the bulk-liquid-vacuum interface decreases slowly with a spatial extension of -5 A [4,5]. Besides, a small increase in the density next to the two solid layers is expected due to the van der Waals interaction with the substrate.…”

Section: Ripplons In 4 He Films Observed By Neutron Scatteringmentioning

confidence: 99%

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Ripplons inHe4films observed by neutron scattering

et al. 1992

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Section: Ripplons In 4 He Films Observed By Neutron Scatteringmentioning

confidence: 99%

Section: Ripplons In 4 He Films Observed By Neutron Scatteringmentioning

confidence: 99%

Ripplons inHe4films observed by neutron scattering

et al. 1992

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“…These earlier works have been followed by many others. [14][15][16][17][18][19][20][21] It was soon determined that the highly layered nature of the liquid film 2 allowed certain of these new modes to be identified as propagating within individual layers. [22][23][24] The modes were termed ''layer phonons.…”

Section: Introductionmentioning

confidence: 99%

Excitations in a thin liquidHe4film from inelastic neutron scattering

et al. 1996

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We perform a thorough analysis of the experimental dynamic structure function measured by inelastic neutron scattering for a low-temperature (Tϭ0.65 K͒ four-layer liquid 4 He film. The results are interpreted in light of recent theoretical calculations of the ͑nonvortex͒ excitations in thin liquid Bose films. The experimental system consists of four outer liquid layers, adsorbed to two solid inner 4 He layers, which are themselves adsorbed to a graphite substrate. Relatively intense surface ͑ripplon͒ and bulklike modes are observed. The analysis of the experimental data gives strong evidence for still other modes and supports the long-standing theoretical predictions of layerlike modes ͑layer phonons͒ associated with excitations propagating primarily within the liquid layers comprising the film. The results of the analysis are consistent with the occurrence of level crossings between modes, and the existence of a layer modes for which the theory predicts will propagate in the vicinity of the solid-liquid interface. The theory and experiment agree on the detailed nature of the ripplon; its dispersion at low momenta, its fall off in intensity at intermediate momenta, and the level crossings at high momentum. Similar to experiment, the theory yields an intense mode in the maxon-roton region which is intrepreted as the formation of the bulklike excitation.

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“…Solutions of these dispersion relations provide bound and continuum states. [30][31][32] Furthermore, according to the discussions of Refs. 10,13,22,24,25 energies ប (q) of bound states should be lower than the separation energy ⑀ S (q) corresponding to the emission of a free 4 He atom into a vacuum:…”

Section: A Nature Of the Eigenstatesmentioning

confidence: 99%

“…As an example of the application of a different approach in order to describe the inhomogeneous free 4 He surface at temperature Tϭ0 we can mention the paper of Ji and Wortis. 32 These authors have used a semiphenomenological Landau model to interpret surface phenomena and put a special emphasis in the analysis of continuum states of the excitation spectrum. On the other hand, the CBF method has been applied to get information about excitations of symmetric finite films at vanishing temperature in.…”

Section: Introductionmentioning

confidence: 99%

Properties of bound, resonant, and regular continuum states of the excitation spectrum of symmetric liquidHe4films atT=0 K

Szybisz

1996

Phys. Rev. B

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Elementary excitations in rather thick symmetric films of liquid 4 He at Tϭ0 K are investigated. They are characterized by a momentum បq parallel to the surface and may be described by bound or continuum states, which are obtained by solving a Bogoliubov-type equation formulated within the framework of the pairedphonon analysis and the hypernetted-chain approximation. Films of coverages n c ϭ0.3 and 0.4 Å Ϫ2 confined by simple Gaussian potentials are studied. The excitation spectrum is numerically evaluated by discretizing the associated eigenvalue problem in a finite box. The evolution of the energy levels as a function of the box size is explored. Examples of the calculated energies and wave functions are displayed in a series of figures. Two differing sorts of continuum states may be distinguished. Depending on the behavior of their excitation energies as a function of the box size on the one hand, and the spatial distribution of their wave functions inside the film and in the asymptotic region far apart from the interface layer on the other, the continuum solutions can be separated into two classes of excitations: ͑a͒ the ''regular'' continuum states and ͑b͒ the ''resonant modes.'' The matrix elements of the particle-hole potential and the penetration factors of the most important states are examined. The lowest-lying branch of states is always bound and for qϽq R (q R Ӎ1.9 Å Ϫ1 being the momentum at the roton minimum͒ it describes surface ripplon excitations. In the atomic scale regime, 1.1 Å Ϫ1 ϽqϽq R , the hardest ''resonant mode'' can be interpreted as a roton trapped at the center of the film and therefore associated with ''bulk'' excitations of the system. Our results support the occurrence of the repulsion between ''bulk'' and ripplon excitations proposed by Pitaevskii and Stringari. The strength of contributions originated from different normal modes to the liquid structure function is evaluated. While for very small values of momenta (qр0.2 Å Ϫ1 ) the contribution of the lowest-lying normal mode is dominant, for momenta qϾq R the structure factor is determined by the contributions originated from the three lowest-lying even states. At qϷq R there is a dramatic transfer of strength from the bound continuation of the hardest ''resonant mode'' to the ripplon excitation. Experimental data of the inelastic structure factor S(q,ប) may be satisfactorily interpreted on the basis of our calculation. On the other hand, it is shown that for 2.9рqр3.9 Å Ϫ1 the lowest-lying excitations become surface modes again.

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Landau model for superfluid films and interfaces atT=0: Local interactions

Cited by 28 publications

References 36 publications

Ripplons inHe4films observed by neutron scattering

Ripplons inHe4films observed by neutron scattering

Excitations in a thin liquidHe4film from inelastic neutron scattering

Properties of bound, resonant, and regular continuum states of the excitation spectrum of symmetric liquidHe4films atT=0 K

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