Multiple Diffusion-Freezing Mechanisms in Molecular-Hydrogen Films

Molecular hydrogen is a fascinating candidate for novel bosonic and fermionic superfluids. We have studied diffusion dynamics of thin films of H_{2}, HD, and D_{2} adsorbed on a glass substrate by measurements of elasticity. The elasticity shows multiple anomalies well below the bulk triple point te...

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Bibliographic Details
Published in:Physical review letters 2019-12, Vol.123 (24), p.245301-245301, Article 245301
Main Authors: Makiuchi, T, Yamashita, K, Tagai, M, Nago, Y, Shirahama, K
Format: Article
Language:English
Subjects:
Anomalies
Elasticity
Fluids
Freezing
Glass substrates
Hydrogen
Phase transitions
Quantum tunnelling
Superfluidity
Surface diffusion
Surface layers
Thermal diffusion
Thin films
Vacancies
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Summary:Molecular hydrogen is a fascinating candidate for novel bosonic and fermionic superfluids. We have studied diffusion dynamics of thin films of H_{2}, HD, and D_{2} adsorbed on a glass substrate by measurements of elasticity. The elasticity shows multiple anomalies well below the bulk triple point temperature. They are attributed to three different diffusion mechanisms of admolecules and their "freezing" into a localized state: classical thermal diffusion of vacancies, quantum tunneling of vacancies, and diffusion of molecules in the uppermost surface. The surface diffusion is active down to 1 K, below which the molecules become localized. This suggests that the surface layer of hydrogen films is on the verge of quantum phase transition to a superfluid state.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.123.245301