Nucleation and Avalanche of 4He Crystals in Aerogel

Dynamical transition of 4 He crystals in aerogel was reported recently (Nomura et al. Phys. Rev. Lett. 101:175703, 2008 ). Bare aerogel, which was placed in the bulk 4 He crystals, was used in the report. 4 He crystals inside the aerogel grew via creep at high temperatures and via avalanche at low t...

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Bibliographic Details
Published in:Journal of low temperature physics 2010-02, Vol.158 (3-4), p.490-495
Main Authors: Ueno, Ken-ichi, Masumoto, Ryota, Mimori, Tomohiro, Osawa, Aiko, Nomura, Ryuji, Okuda, Yuichi
Format: Article
Language:English
Subjects:
Aerogels
Avalanches
Characterization and Evaluation of Materials
Condensed Matter Physics
Contact
Crystallization
Crystals
Density
Liquids
Magnetic Materials
Magnetism
Nucleation
Physics
Physics and Astronomy
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Summary:Dynamical transition of 4 He crystals in aerogel was reported recently (Nomura et al. Phys. Rev. Lett. 101:175703, 2008 ). Bare aerogel, which was placed in the bulk 4 He crystals, was used in the report. 4 He crystals inside the aerogel grew via creep at high temperatures and via avalanche at low temperatures owing to the competition between thermal fluctuation and quenched disorder. Crystal-liquid interface advanced from the edge to inside of the aerogel. Crystal has a greater density than liquid so that the extra mass has to be transported in the crystallization process. It is not known how the mass is transported in the aerogel. To find a clue to this issue, we did an experiment with aerogel in a glass tube so that the aerogel had contact with the bulk on only one surface. In this case, a similar dynamical transition was observed at low temperatures. In the avalanche region, however, 4 He crystals did not grow from the outer surface of the aerogel but nucleated at various sites inside the aerogel. This means that crystallization in aerogel does not occur by the forced invasion of 4 He crystal but by a process of the bulk crystal once being melted and transported to increase the pressure of the liquid in the aerogel. Thus, a mass transport mechanisms for the crystallization has been revealed by this observation.
ISSN:0022-2291
1573-7357
DOI:10.1007/s10909-009-9933-8