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arXiv · 1904.02269

Second layer crystalline phase of helium films on graphite

Saverio Moroni·Massimo Boninsegni
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Abstract

We investigate theoretically the existence at low temperature of a commensurate (4/7) crystalline phase of a layer of either He isotope on top of a He-4 layer adsorbed on graphite. We make use of a recently developed, systematically improvable variational approach which allows us to treat both isotopes on an equal footing. We confirm that no commensurate crystalline second layer of He-4 forms, in agreement with all recent calculations. Interestingly and more significantly, we find that even for He-3 there is no evidence of such a phase, as the system freezes into an {\it incommensurate} crystal at a coverage lower than that (4/7) at which a commensurate one has been predicted, and for which experimental claims have been made. Implications on the interpretation of recent experiments with helium on graphite are discussed.

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Saverio Moroni, Massimo Boninsegni. 2019-05-24. Second layer crystalline phase of helium films on graphite. https://doi.org/10.1103/physrevb.99.195441

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