Second layer crystalline phase of helium films on graphite

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.

arXiv comment7 pages, 4 figures in color

References in corpus (8)

• Supersolids: what and where are they ?
• Twist-averaged Boundary Conditions in Continuum Quantum Monte Carlo
• Phase diagram of 4He adsorbed on graphite
• Role of Bose Statistics in Crystallization and Quantum Jamming
• Nonlinear Network description for many-body quantum systems in continuous space
• Possible quantum liquid crystal phases of helium monolayers
• Equation of state of two--dimensional ${}^3$He at zero temperature
• Low-density phases of ${}^3$He monolayers adsorbed on graphite

Cited by in corpus (7)

• Spatially Modulated Superfluid State in Two-Dimensional ${}^4$He Films
• Thermodynamic properties of an $S=1/2$ ring-exchange model on the triangular lattice
• Specific heat of thin ${}^4$He films on graphite
• Superfluid transition of the second layer of He-4 on graphite: does substrate corrugation matter?
• Phase diagram and crystal melting of helium-4 in two dimensions
• He-4 monolayer on Graphene: a Quantum Monte Carlo study
• On the Novel Superfluidity in the Second Layer of ${}^4$He on Graphite