Critical Surface Density of the Superfluid Component 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

Sound propagation has been studied in He H films adsorbed on alumina powder grains (Ale03). Sound velocity and adsorption isotherm data provide evidence that surface tension forces can exceed the van der Waals forces as the film thickness increases. A model of capillary condensation at the points wherethe powder grains touch accounts for many of the qualitative features of the data. The surface tension sound velocity decreases with increasing powder grain size.

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“…Coz (15) ?/ Then at higher temperatures the fifth-sound velocity can be obtained from the measured c and Co,…”

Section: (C;+c~)mentioning

confidence: 99%

Surface tension sound in superfluid helium films adsorbed on alumina powder

et al. 1979

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“…For instance, the prototype experiment on copper 1 showed that muons are mobile above 100 K and at lower temperatures are localized at fixed interstitial sites, later identified as octahedral. 2 Experiments carried out a year ago demonstrated that muons can also be localized in aluminum by adding substitutional impurities 3 ' 4 or by creating defects by irradiation 5 or thermal treatment. 6 One remaining question is whether the muon is "frozen in" at still lower temperatures in pure aluminum.…”

Section: + Tsmentioning

confidence: 99%

Third-Sound Velocity and Onset on Grafoil

1980

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is sometimes overlooked, when insufficient care is taken in specifying the variable that is to be identified with the chemical potential. This point is discussed in Ref. 4. In addition, because of the vector character of the 3 He-A order parameter, there is an explicit term proportional to f° V x v" in the equation governing the time rate of change of the effective phase. This additional term is strongly emphasized in Ref. 1, but the first term is also implicit in their discussion and can produce fully comparable effects. 8 We emphasize that this circulation (which is the hydrodynamical manifestation of the crucial nonuniformity in the initial order parameter) is essential for the appearance of the gauge-wheel effect. The circulation distinguishes this geometry from ordinary superfluid couette-flow experiments, which are not necessarily carried out against a fixed background supercurrent. 9 The same effect will take place in the A phase of superfluid helium-3 in the presence of a circulating supercurrent, even when the anisotropy axis is radial. 10 In a nonlinear analysis the heat current at the opposite wall is determined by the bulk entropy production. In a linear analysis the entropy production is second order and the thermal current can be taken to vanish for all x.u We use these in the form given by I. M. Khalatnikov, An Introduction to the Theory of Superfluidity (Benjamin, New York, 1965), p. 66.We use the symbol /Lt s to denote what Khalatnikov denotes by the symbol pi. Since whatever name one gives it, the quantity is determined by the hydrodynamics, this change in nomenclature has no consequence for our analysis. However we shall show in Ref. 4 that what is conventionally called the chemical potential in many treatments of superfluid hydrodynamics is, in fact, the chemical potential in the local rest frame of the superfluid ix a . This differs from the true chemical potential IJL by terms of second order in v n and v s O-i 3^ +iv s 2 -v" ° v 5 ) and for many purposes j* and p s can be identified. In the case of gauge-wheel effects the secondorder terms are of crucial importance, and one loses considerable insight into the underlying physics by confusing pt 5 with \k. In particular, the fact that the twofluid hydrodynamics gives a constant \k s is not incompatible with our earlier assertion that the phase winding is balanced by a (true) chemical-potential gradient in the steady state. 13 This does not necessarily imply that the temperature drop remains unmeasurably small as w increases, though when w/v » 1, the fluid may respond through vortex nucleation rather than by producing a chemical potential (and hence temperature) drop. Note that from this point of view gauge-wheel effects are cleaner in 4 He than in 3 He-A, since the possibility for similar complications due to textural motions is absent in the more common superfluid.

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“…Superfluid onset with the universal jump of the superfluid density in the third-sound experiment [3] suggested the transition was due to the Kosterlitz-Thouless mechanism [5], where 2D superfluid vortices play a main role. Below the 2D KT transition temperature T KT , all 2D vortices are bound into pairs.…”

Section: Measurement-frequency Dependence Of 2d Superfluid Onsetmentioning

confidence: 99%

“…In contrast to this three-dimensional (3D) 4 He fluid, a mathematical proof indicates no long-range-ordering in 2D and 1D at any finite temperature [2]. However, literally 2D 4 He film formed on a flat solid surface was found to show a superfluid onset [3,4]. The onset was understood as the Kosterlitz-Thouless (KT) transition [5].…”

Section: Introductionmentioning

confidence: 99%

Observation of superfluidity in two- and one-dimensions

Wada

Hieda

Toda

et al. 2013

Low Temperature Physics

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Even though there is no long-range-ordered state of a superfluid in dimensions lower than the threedimension (3D) such as bulk 4 He liquid, superfluidity has been observed for flat 4 He films in 2D and recently for nanotubes of 4 He in 1D by the torsional oscillator method. In the 2D state, in addition to the superfluid below the 2D Kosterlitz-Thouless transition temperature T KT , superfluidity is also observed in a normal fluid state above T KT , which depends strongly on the measurement frequency and the system size. In the 1D state of the nanotubes, superfluidity is directly observed as a frequency shift in the torsional oscillator experiment. Some calculations suggest a superfluidity of a 1D Bose fluid with a finite length, where thermal excitations of 2 -phase winding play the main role for superfluid onset of each tube. Dynamics of the 1D superfluidity is also suggested by observing the dissipation in the torsional oscillator experiment.

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Critical Surface Density of the Superfluid Component inHe4Films

Cited by 193 publications

References 4 publications

Surface tension sound in superfluid helium films adsorbed on alumina powder

Surface tension sound in superfluid helium films adsorbed on alumina powder

Third-Sound Velocity and Onset on Grafoil

Observation of superfluidity in two- and one-dimensions

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