Low-temperature heat-capacity measurements of<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 adsorbed on a disordered substrate

Tait, R. H.; Reppy, J. D.

doi:10.1103/physrevb.20.997

Cited by 53 publications

(22 citation statements)

References 54 publications

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“…37,42,43 The Vycor with the largest pore diameter ͑Vycor29, Corning code 7930͒ was previously measured and characterized by Tait 28,37 who performed gas adsorption experiments to determine a mass density for Vycor29 of 72% the value of bulk a-SiO 2 and an average pore diameter of 7-8 nm. The remaining Vycor samples were supplied to us by Maris who obtained them from Elmer of the Corning Research Laboratory.…”

Section: Experimental Mattersmentioning

confidence: 99%

“…An interpretation of both observations in terms of the Tunneling Model would require that the energy-independent spectral density P of the tunneling states increases with increasing porosity ͑reaching a saturation at the very largest porosities͒, in order to explain the increase of the specific heat, while their coupling strength to the phonons decreases so as to keep the thermal-conductivity constant. The Cornell authors 27,28,32,37 were skeptical of such an interpretation and suggested instead that one should consider the possible role of localized excitations either of surface atoms or of adsorbed gases. Their vibrational excitations would be seen in specific heat but might not couple strongly to the phonons.…”

Section: Introductionmentioning

confidence: 99%

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Low-energy lattice vibrations of porous silica glass

Watson

Pohl

2003

Phys. Rev. B

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Internal friction, speed of sound, and thermal conductivity of Vycor glass with porosities ranging from 29% to 36% have been measured from 65 mK to 300 K. The results have been compared with those obtained on bulk amorphous silica in order to understand how the porous structure affects the low-energy tunneling states. Contrary to specific-heat results reported previously on Vycor, our measurements indicate that these changes are surprisingly small. Our findings agree qualitatively with the results reported previously on sol-gel porous glass with a similar porosity, and also on aerogels, which are even more highly porous than Vycor. Analysis of the porous silica data suggests that the porosity has very little influence on the spectral density of the tunneling defects, while their coupling energy to the phonons scales with the speed of sound. The excitations observed in specific heat, however, appear to be different from those observed in the acoustic and thermal-conductivity experiments.

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Section: Experimental Mattersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Low-energy lattice vibrations of porous silica glass

Watson

Pohl

2003

Phys. Rev. B

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“…1, is the systematic crossing of the specific heat curves at lower temperatures as the helium coverage is reduced. This is the first hint of a dramatic dependence of the thin film heat capacity on coverage in the 4He-Vycor system, which will be most evident in measurements carried out at temperatures below 0.5 K. 13 In the 1970s the picture began to change. Kiewiet et al 14 measured the superfluid density for helium contained in porous Vycor glass utilizing a fourth sound technique.…”

Section: Superfluid Helium Experiments In Vycor Glassmentioning

confidence: 99%

Superfluid helium in porous media

1992

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The superfluid properties of 4He absorbed in porous media are discussed. Emphasis is given to the nature of the superjluid transition for helium contained in a variety of different porous structures. Recent heat capacity and superfluid measurements for helium in Vycor glass and other porous media are presented in some detail. The onset of superfluidity as a function of adsorbed helium coverage at zero temperature, or "boson localization," is touched on briefly. The problem of dissipation of superflow in porous media, especially in the vicinity of the superfluid transition, is discussed.

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“…Torii et al 4 reported a ''phase'' diagram of H 2 in Vycor glass which is quite similar to that of 4 He in Vycor glass. 12 In the case of 4 He, it contains a superfluid phase. Brewer et al 5 have measured the heat capacity of H 2 in porous Vycor glass ͑typical R p Ϸ3 nm͒ at 4 K ϽTϽ15 K. They observed an anomalous behavior and interpreted it as a possible indication of a superfluid transition of H 2 at around 9.6 K. We have already presented some of the results discussed in this paper in a short communication: It focused on the search for a possible superfluid transition of H 2 in Vycor glass.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen in porous Vycor glass

et al. 1996

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Hydrogen in porous Vycor glass ͑pore radius R p ϭ3.0 nm͒ has been investigated with a torsional oscillator technique at 7.5 K рTр 22 K. H 2 molecules which are adsorbed in Vycor at TϾT 3 (T 3 , triple point of bulk H 2 ) leave the Vycor when decreasing the temperature to below a characteristic value T c рT 3 ; T c depends on the amount of H 2 in the Vycor. This interpretation of the data is supported by simultaneous measurements of the H 2 vapor pressure. A similar phenomenon is observed with a capacitor filled with Vycor into which H 2 is condensed. We conclude that the free energy of solid H 2 in the Vycor is larger than that of bulk solid H 2 . Information on the free energy of H 2 confined in the Vycor is important to understand the depression of its freezing temperature in restricted geometries. We also discuss the properties of solids and the depression of their freezing temperature in restricted geometries.

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Low-temperature heat-capacity measurements ofHe4films adsorbed on a disordered substrate

Cited by 53 publications

References 54 publications

Low-energy lattice vibrations of porous silica glass

Low-energy lattice vibrations of porous silica glass

Superfluid helium in porous media

Hydrogen in porous Vycor glass

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