Excitations in a thin liquid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>film from inelastic neutron scattering

Clements, B. E.; Godfrin, H.; Krotscheck, E.; Läuter, H.; Leiderer, Paul; Passiouk, Valeria; Tymczak, C. J.

doi:10.1103/physrevb.53.12242

Cited by 46 publications

(59 citation statements)

References 29 publications

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“…This is the beginning of layer formation around the high density in the trough. Calculations of the helium density adjacent to porous media walls shows clear layer formation [19][20][21] .…”

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confidence: 99%

Localization of Bose–Einstein Condensation by Disorder

2006

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Recent experiments suggest that Bose-Einstein condensation (BEC) in liquid 4 He can be localized when the liquid is confined in porous media. We demonstrate in a simple model of hard core bosons using Monte Carlo that the condensate can be separated into two parts. The two regions of condensate are separated by a region of uncondensed fluid that forms in response to a local attractive external potential. The aim is to illustrate that separated condensates, and therefore localized BEC, can be created in porous media.

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Section: Resultsmentioning

confidence: 99%

Localization of Bose–Einstein Condensation by Disorder

2006

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“…Experimental information is available about the scattering of helium atoms from helium surfaces and films [1][2][3][4][5]; from the dynamics of localized excitations within the fluid, including excitation scattering from the surface and quantum evaporation [5][6][7][8] ; and from inelastic neutron scattering at grazing angles from adsorbed films [9][10][11][12]. Moreover, information about the condensate fraction in helium may be obtainable directly from elastic transmission of 4 He atoms through superfluid 4 He slabs [13].…”

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Quantum Sticking, Scattering, and Transmission ofH4eatoms from SuperfluidH
Campbell¹,
Krotscheck
²
,
Saarela
³

1998
Phys. Rev. Lett.
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We develop a microscopic theory of the scattering, transmission, and sticking of 4 He atoms impinging on a superfluid 4 He slab at near normal incidence, and inelastic neutron scattering from the slab. The theory includes coupling between different modes and allows for inelastic processes. We find a number of essential aspects that must be observed in a physically meaningful and reliable theory of atom transmission and scattering; all are connected with multiparticle scattering, particularly the possibility of energy loss. These processes are (a) the coupling to low-lying (surface) excitations (ripplons/third sound) which is manifested in a finite imaginary part of the self energy, and (b) the reduction of the strength of the excitation in the maxon/roton region. The dynamics of liquid4 He films and the bulk fluid near its free surface continues to be of considerable interest. Experimental information is available about the scattering of helium atoms from helium surfaces and films [1][2][3][4][5]; from the dynamics of localized excitations within the fluid, including excitation scattering from the surface and quantum evaporation [5][6][7][8] ; and from inelastic neutron scattering at grazing angles from adsorbed films [9][10][11][12]. Moreover, information about the condensate fraction in helium may be obtainable directly from elastic transmission of 4 He atoms through superfluid 4 He slabs [13]. The fact that helium slabs have been made in the laboratory [14] leads to the prospect that the dynamic probes previously applied to adsorbed films and bulk surfaces of helium can now be applied to slabs. The slabs should produce simpler and thus easier to interpret results than the adsorbed films.We report here on the results of a manifestly microscopic theoretical analysis of the dynamics of such a slab at zero temperature. We find that atom scattering processes are dominated by multi-particle events, particularly the coupling to ripplons. This is in qualitative agreement with the conclusions of Edwards and collaborators [1][2][3][4] in their results for the related helium atom scattering from the free surface of bulk helium. Our results not only provide insight into the transmission and sticking of a helium beam that was not previously available from theory or experiment, it also provides detailed predictions for the anticipated experiments on slabs.The theoretical method used here has been successfully applied to the bulk [15,16], to adsorbed films [17,18] and to droplets [19]; in the latter two it was successful in making detailed and correct predictions about surface states (ripplons and third sound) which also play a very important role in the slab geometry. The theory is adapted here to the slab geometry, including scattering states. We outline our theory and present some illuminating results waves for at non-normal incidence which also provide insights into quantum evaporation.We consider the ground state of a slab of superfluid 4 He of particle number 1.5Å−2 , corresponding to a thickness of approximately 80Å,...

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“…However, the layered roton line width in helium films on aerogel shows a pronounced broadening with respect to that found in helium films on graphite. 61.12.Ex Surface excitations were first measured on graphite [1,2] and modelled using a many-body theory [3]. The excitations present in very thin films are composed of ripplons and layered rotons.…”

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Surface excitations in thin helium films on silica aerogel

Läuter

Bogoyavlenskii

Puchkov

et al. 2002

Applied Physics A: Materials Science & Processing

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Abstract. First measurements are reported on pure surface excitations in thin superfluid 4 He films on silica aerogel. The ripplon dispersion curve is found to be the same for helium on graphite and silica aerogel substrates. However, the layered roton line width in helium films on aerogel shows a pronounced broadening with respect to that found in helium films on graphite. 61.12.Ex Surface excitations were first measured on graphite [1,2] and modelled using a many-body theory [3]. The excitations present in very thin films are composed of ripplons and layered rotons. The ripplon is an excitation of the liquid-gas interface of the film, while the layered roton is an excitation bound to the layered structure of the liquid film itself. In the case of a very thin film only one layered structure and one layered roton exist adjacent to the solid-liquid interface. The liquid film is formed on top of a solid helium layer: on graphite, for instance, firstly two solid layers of helium are formed upon condensing helium in the sample. These solid layers also exist on aerogel substrate, but they are strongly modified due to the heterogeneous surface of this substrate. On a given substrate one can find a coverage of helium at which only the two above-mentioned excitations, ripplons and layered rotons, exist, i.e. no bulk excitations, e.g. phonons, maxons or rotons are observed. The ripplon dispersion relation is determined by the liquid-gas-interface properties, and therefore it shows essentially the same behaviour on graphite and on silica aerogel. On the other hand, the properties of the layered roton are expected to be affected by the nature of the solid-liquid interface; they are most conveniently determined at this particular coverage. The layered roton gap energy is determined by the substrate-helium interaction [3]; the curvature reflects its two-dimensional character through the liquid structure factor and the effective mass [3,4]; and its line width is anomalously broad. The last feature may have importance in relation to the bulk helium behaviour in aerogel, seen * Corresponding author. (Fax: +33-476/207120, E-mail: lauter@ill.fr) when the aerogel is filled with helium, because the temperature dependence of the superfluid component shows near the lambda transition a different exponent with respect to helium in graphite [5]. PACS:

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Excitations in a thin liquidHe4film from inelastic neutron scattering

Cited by 46 publications

References 29 publications

Localization of Bose–Einstein Condensation by Disorder

Localization of Bose–Einstein Condensation by Disorder

Quantum Sticking, Scattering, and Transmission ofH4eatoms from SuperfluidH
Campbell¹,
Krotscheck
²
,
Saarela
³

1998
Phys. Rev. Lett.
Self Cite
26
1
12
0
View full text Add to dashboard Cite

Surface excitations in thin helium films on silica aerogel

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Excitations in a thin liquidHe4film from inelastic neutron scattering

Cited by 46 publications

References 29 publications

Localization of Bose–Einstein Condensation by Disorder

Localization of Bose–Einstein Condensation by Disorder

Quantum Sticking, Scattering, and Transmission ofH4eatoms from SuperfluidHCampbell1, Krotscheck2, Saarela3 1998Phys. Rev. Lett.Self Cite261120View full textAdd to dashboardCite

Surface excitations in thin helium films on silica aerogel

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Quantum Sticking, Scattering, and Transmission ofH4eatoms from SuperfluidH
Campbell¹,
Krotscheck
²
,
Saarela
³

1998
Phys. Rev. Lett.
Self Cite
26
1
12
0
View full text Add to dashboard Cite