Abstract
We use optical methods to study condensation of 4He into a 95% porosity silica aerogel at temperatures below the bulk critical point. Simugtaneous pressure and optical measurements are performed along isotherms, as the cell is very slowly filled or emptied. We find that the pressure presents a quasiplateau below the bulk saturation pressure P sat over a finite range of densities inside the aerogel. In this range, strong light scattering is observed, which shows that the helium density fluctuates on a microscopic scale. Quantitative analysis shows that the helium density is correlated over distances somewhat larger than the gel correlation length. We discuss our resugts in terms of two possible scenarios, capillary condensation and liquid-gas transition.
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Lambert, T., Gabay, C., Puech, L. et al. Optical Study of 4He Condensation into a Silica Aerogel. Journal of Low Temperature Physics 134, 293–302 (2004). https://doi.org/10.1023/B:JOLT.0000012569.91725.5d
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DOI: https://doi.org/10.1023/B:JOLT.0000012569.91725.5d