Superfluidity of quasi-2D 4He droplets on graphite

The superfluid response of nanoscale size quasi-2D 4He droplets adsorbed on a graphite substrate is investigated by computer simulations. It is found that clusters comprising as few as 7 atoms are stable at temperatures of ≲0.15 K. Clusters of ∼20 atoms or less are liquid-like and ∼100% superfluid. As the size is increased, the central region crystallizes, forming the commensurate C1/3 phase, with a quasi-1D surface layer of superfluidity possibly evolving into a Luttinger liquid or a transverse quantum superfluid with increasing cluster size. The relevance to quasi-2D molecular spectroscopy is discussed.