Second-layer crystalline phase of helium films on graphite

Saverio Moroni and Massimo Boninsegni
Phys. Rev. B 99, 195441 – Published 22 May 2019

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 He4 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 He4 forms, in agreement with all recent calculations. Interestingly and more significantly, we find that even for He3 there is no evidence of such a phase, as the system freezes into an 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 for the interpretation of recent experiments with helium on graphite are discussed.

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  • Received 5 April 2019

DOI:https://doi.org/10.1103/PhysRevB.99.195441

©2019 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Saverio Moroni

  • CNR-IOM Democritos, Istituto Officina dei Materiali and Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste, Italy

Massimo Boninsegni*

  • Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1

  • *m.boninsegni@ualberta.ca

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Vol. 99, Iss. 19 — 15 May 2019

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