Anisotropic superfluidity of 4He on a C36 fullerene molecule

We have performed path-integral Monte Carlo calculations to study the adsorption of He-4 atoms on two different C-36 isomers with the D-6h and the D-2d symmetries. The radial He-4 density distributions reveal layer-by-layer growth with the first layer being located at a distance of similar to 5.5 angstrom from the C-36 molecular center and the second layer at similar to 8.3 angstrom. From the angular density profiles of He-4, we find different quantum states as the number of He-4 adatoms N varies. For N = 20, we observe commensurate solid structures on both D-6h and D-2d isomers, where each of 8 hexagon and 12 pentagon centers of the fullerene surfaces is occupied by a single He-4 atom. The second-layer promotion starts beyond N = 38 on both isomers, where a compressible incommensurate structure is observed on the D-6h isomer and another commensurate structure on D-2d. Between N = 20 and N = 38, the He-4 monolayer on D-6h shows several distinct rings of delocalized He-4 atoms along with strongly anisotropic superfluid responses at low temperatures, while isotropic but weak superfluid responses are observed in the He-4 layer on D2d. (C) 2015 AIP Publishing LLC.