Division of Quantum Phases and Devices, School of Physics, Konkuk University, Seoul 143-701, South Korea.
J Chem Phys. 2012 Feb 14;136(6):064514. doi: 10.1063/1.3685848.
Path-integral Monte Carlo calculations have been performed to study (4)He adsorption on a single C(60) molecule. Helium corrugations on the fullerene molecular surface are incorporated with the (4)He-C(60) interaction described by the sum of all (4)He-C interatomic pair potentials. Radial density distributions show a layer-by-layer growth of (4)He with the first adlayer being located at a distance of ~6.3 Å from the center of the C(60) molecule. The monolayer shows different quantum states as the number of (4)He adatoms N varies. For N = 32, we find a commensurate solid, with each of the 32 adsorption sites on the molecular surface being occupied by a single (4)He atom. Various domain-wall structures are observed as more (4)He atoms are added and the first layer crystallizes into an incommensurate solid when it is completely filled. This commensurate-incommensurate transition of the helium monolayer is found to be accompanied by re-entrant superfluid response at a low temperature of 0.31 K with the superfluidity being totally quenched at N = 32, 44, and 48. Finally, the different quantum states observed in the helium monolayer around C(60) are compared with phase diagrams proposed for the corresponding layer on a graphite surface.
已进行路径积分蒙特卡罗计算，以研究（4）He 在单个 C（60）分子上的吸附。富勒烯分子表面上的氦波纹与由所有（4）He-C 原子间对势能之和描述的（4）He-C（60）相互作用相结合。径向密度分布显示（4）He 的逐层生长，第一吸附层位于 C（60）分子中心的~6.3 Å 距离处。单层显示出不同的量子态，因为（4）He 吸附原子 N 的数量不同。对于 N = 32，我们发现了一个具有公度的固体，分子表面上的 32 个吸附位中的每一个都被一个（4）He 原子占据。随着更多（4）He 原子的加入，观察到各种畴壁结构，并且当第一层完全填充时，第一层结晶成非公度固体。发现氦单层的这种公度-非公度转变伴随着在低温 0.31 K 下的再入超流响应，当 N = 32、44 和 48 时，超流性完全被抑制。最后，将在 C（60）周围的氦单层中观察到的不同量子态与相应的石墨表面上的层的相图进行比较。
