Ripplons in<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>films observed by neutron scattering

Läuter, H.; Godfrin, H.; Frank, V.; Leiderer, Paul

doi:10.1103/physrevlett.68.2484

Cited by 88 publications

(83 citation statements)

References 7 publications

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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].…”

mentioning

confidence: 99%

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

1998
Phys. Rev. Lett.
26
1
12
0
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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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mentioning

confidence: 99%

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

1998
Phys. Rev. Lett.
26
1
12
0
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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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confidence: 99%

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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“…In porous media 19,[21][22][23][24]26,[28][29][30][31]34 and in helium films, 35,38,39 a layer mode is also observed. This is a mode that propagates in the 1-4 liquid layers adjacent to the porous media walls.…”

Section: Figmentioning

confidence: 88%

“…At a significantly higher pressure (34 bar) a small mode width at T = 0.2 K in MCM-41 (47Å diameter) has been observed. 30 At partial filling of porous media 28,34 and in helium films on surfaces 35,36 , the P-R mode energies differ from the bulk values. At partial filling the P-R mode energy is lower at wave vectors Q ≃ 1Å −1 (the maxon region) and higher in the roton region 18,37 as if the films have a lower density than the bulk density.…”

Section: Figmentioning

confidence: 99%

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

et al. 2013

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We present neutron scattering measurements of the phonon-roton (P-R) mode of superfluid 4 He confined in 47 Å MCM-41 at T = 0.5 K at wave vectors, Q, beyond the roton wave vector (QR = 1.92 Å−1 ). Measurements beyond the roton require access to high wave vectors (up to Q = 4 Å−1 ) with excellent energy resolution and high statistical precision. The present results show for the first time that at T = 0.5 K the P-R mode in MCM-41 extends out to wave-vector Q ≃ 3.6 Å−1 with the same energy and zero width (within precision) as observed in bulk superfluid 4 He. Layer modes in the roton region are also observed. Specifically, the P-R mode energy, ωQ, increases with Q for Q > QR and reaches a plateau at a maximum energy ωQ = 2∆ where ∆ is the roton energy, ∆ = 0.74 ± 0.01 meV in MCM-41. This upper limit means the P-R mode decays to two rotons when its energy exceeds 2∆. It also means that the P-R mode does not decay to two layers modes. If the P-R could decay to two layer modes, ωQ would plateau at a lower energy, ωQ = 2∆L where ∆L = 0.60 meV is the energy of the roton like minimum of the layer mode. The observation of the P-R mode with energy up to 2∆ shows that the P-R mode and the layer modes are independent modes with apparently little interaction between them.

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Ripplons inHe4films observed by neutron scattering

Cited by 88 publications

References 7 publications

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

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

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

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

Surface excitations in thin helium films on silica aerogel

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

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Ripplons inHe4films observed by neutron scattering

Cited by 88 publications

References 7 publications

Quantum Sticking, Scattering, and Transmission ofH4eatoms from SuperfluidHCampbell1, Krotscheck2, Saarela3 1998Phys. Rev. Lett.261120View full textAdd to dashboardCite

Quantum Sticking, Scattering, and Transmission ofH4eatoms from SuperfluidHCampbell1, Krotscheck2, Saarela3 1998Phys. Rev. Lett.261120View full textAdd to dashboardCite

Surface excitations in thin helium films on silica aerogel

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

Contact Info

Product

Resources

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

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

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

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