▎ 摘　　要

Path-integral Monte Carlo calculations have been performed to study the correlation between two He-4 monolayers adsorbed on opposite sides of a graphene sheet. Here, the He-4-substrate interaction is described by the pairwise sum of the He-4-C interatomic potentials. We employ two different anisotropic He-4-C pair potentials proposed to fit the helium scattering data on a graphite surface, namely, a 6-12 Lennard-Jones potential and a Yukawa-6 potential. With the Lennard-Jones substrate potential, we do not observe any noticeable correlation between two oppositeside He-4 monolayers, which is consistent with the prediction of the previous theoretical studies based on the same substrate potential. When the Yukawa-6 substrate potential is used, however, two incommensurate triangular solids, which are realized at the first-layer completion density of 0.12 (-2), are found to favor an AA stacking order, two triangular lattices on top of each other, over an AB stacking. Finally, the effects of this interlayer correlation on the formation of stable mobile vacancies are discussed.