Superfluid helium in porous media

Reppy, J. D.

doi:10.1007/bf00114905

Cited by 195 publications

(228 citation statements)

References 51 publications

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“…1 at n = n c and therefore makes a distinction between the "solid" part of the film and the "liquid" overlayer, which is superfluid at low temperature. Although this approach, often called the "inert-layer model," is sufficient for interpreting most superflow measurements, 8 it eschews particle statistics by ignoring exchange between the solid layer and the overlying superfluid film. In its most orthodox form, the inert-layer model predicts that the various thermodynamic properties of the superfluid should be extensive with respect to n − n c , where n is the total density of the film.…”

Section: A Bose Insulatorsmentioning

confidence: 99%

Onset of superfluidity inHe4films adsorbed on disordered substrates

1997

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We have studied 4 He films adsorbed in two porous glasses, aerogel and Vycor, using high precision torsional oscillator and DC calorimetry techniques. Our investigation focused on the onset of superfluidity at low temperatures as the 4 He coverage is increased. Torsional oscillator measurements of the 4 He-aerogel system were used to determine the superfluid density of films with transition temperatures as low as 20 mK. Heat capacity measurements of the 4 He-Vycor system probed the excitation spectrum of both non-superfluid and superfluid films for temperatures down to 10 mK. Both sets of measurements suggest that the critical coverage for the onset of superfluidity corresponds to a mobility edge in the chemical potential, so that the onset transition is the bosonic analog of a superconductor-insulator transition. The superfluid density measurements, however, are not in agreement with the scaling theory of an onset transition from a gapless, Bose glass phase to a superfluid. The heat capacity measurements show that the non-superfluid phase is better characterized as an insulator with a gap. 67.40. Rp,64.60.Cn,67.40.Yv

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Section: A Bose Insulatorsmentioning

confidence: 99%

Onset of superfluidity inHe4films adsorbed on disordered substrates

1997

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“…Bosonic systems in disordered potentials have been extensively investigated in the recent past, both experimentally and theoretically [9]. Experiments with superfluid 4 He in porous materials have demonstrated the suppression of superfluid transport and the critical behavior at the phase transition in presence of disorder [10]. From the theoretical point of view a rich variety of phenomena is expected to occur in these systems, among which the most fascinating are Anderson localization, initially proposed in the context of electron transport in disordered solids [11], and later predicted and observed for non-interacting wave phenomena such as light [12,13], and the quantum transition to the Bose glass phase that originates from the interplay of interactions and disorder [14].…”

Section: Introductionmentioning

confidence: 99%

Collective dynamics and expansion of a Bose-Einstein condensate in a random potential

Modugno

2006

Phys. Rev. A

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We investigate the dynamics of a Bose-Einstein condensate in the presence of a random potential created by optical speckles. We first consider the effect of a weak disorder on the dipole and quadrupole collective oscillations, finding uncorrelated frequency shifts of the two modes with respect to the pure harmonic case. This behaviour, predicted by a sum rules approach, is confirmed by the numerical solution of the Gross-Pitaevskii equation. Then we analyze the role of disorder on the onedimensional expansion in an optical guide, discussing possible localization effects. Our theoretical analysis provides a useful insight into the recent experiments performed at LENS [J. Lye et al., Phys. Rev. Lett. 95, 070401 (2005); C. Fort et al., cond-mat/0507144].

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“…There has been considerable interest in studying the superfluid transition for helium in a variety of porous media. [2] One such system is Vycor which is a random glass with a porosity of order 30%. Remarkably, the critical exponent ζ is found to be unchanged by the seemingly huge perturbation represented by the glass.…”

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confidence: 99%

“…Nevertheless no evidence of a cross-over to the uncorrelated disorder regime is evident in the full-pore experiments. [2] Very recently however, Crowell et. al.…”

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Critical Behavior of Superfluid4He in Aerogel

Moon

Girvin

1995

Phys. Rev. Lett.

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We report on Monte Carlo studies of the critical behaviour of superfluid 4 He in the presence of quenched disorder with long-range fractal correlations. According to the heuristic argument by Harris, uncorrelated disorder is irrelevant when the specific heat critical exponent α is negative, which is the case for the pure 4 He. However, experiments on helium in aerogel have shown that the superfluid density critical exponent ζ changes. We hypothesize that this is a cross-over effect due to the fractal nature of aerogel. Modelling the aerogel as an incipient percolating cluster in 3D and weakening the bonds at the fractal sites, we perform XY-model simulations, which demonstrate an increase in ζ from 0.67 ± 0.005 for the pure case to an apparent value of 0.722 ± 0.005 in the presence of the fractal disorder, provided that the helium correlation length does not exceed the fractal correlation length.PACS numbers: 75.40.Mg, 75.10.Nr, 64.60.Ak It is generally believed that the superfluid transition (λ-point) of pure 4 He belongs to the classical 3D-XY model universality class. Near the critical temperature T c , the superfluid density scales as |T − T c | ζ , where ζ is measured [1] to be 0.674 ± 0.003. There has been considerable interest in studying the superfluid transition for helium in a variety of porous media.[2] One such system is Vycor which is a random glass with a porosity of order 30%. Remarkably, the critical exponent ζ is found to be unchanged by the seemingly huge perturbation represented by the glass. This however is the result expected according to heuristic arguments of Harris [3] and more rigorous recent work [4] which shows that weak, uncorrelated randomness is irrelevant at the unperturbed critical point provided that the specific heat exponent is negative. The exponent [1] α ≈ −0.026±0.004 is indeed negative for 4 He, however Narayan and Fisher [5] have argued that since α is only slightly negative, the crossover to the pure 3D XY critical regime is almost logarithmically slow. Until recently Vycor was the only porous medium in which ζ was observed to be unchanged. New experiments however appear to have added a second material, porous gold (which also has short-range correlations), to the list. [6] Remarkable results have been obtained for the aerogel system. Aerogel is a fractal silica 'dust' with porosities of 95-98% or higher. Despite the fact that aerogel is almost entirely empty space, and that it (unlike Vycor) has only a tiny effect on the critical temperature, the exponent ζ is apparently quite distinctly shifted [7,8,6] to approximately 0.75 (or larger), indicating that the nominally weak aerogel perturbation is relevant at the 3D XY critical point and aerogel (perhaps) produces a new universality class. The specific heat data suggests that either hyperscaling is violated or the amplitude ratio is exceptionally small. [9,10] In addition to shifting ζ and α, aerogel dramatically changes the topology of the 3 He-4 He mixture phase diagram. [11,12] It is known that long-range correlati...

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Superfluid helium in porous media

Cited by 195 publications

References 51 publications

Onset of superfluidity inHe4films adsorbed on disordered substrates

Onset of superfluidity inHe4films adsorbed on disordered substrates

Collective dynamics and expansion of a Bose-Einstein condensate in a random potential

Critical Behavior of Superfluid4He in Aerogel

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