A Perspective on Collective Properties of Atoms on 2D Materials

Atoms deposited on 2D electronic materials, such as graphene, can exhibit unconventional many-body correlations, not accessible in other settings. All of these are driven by van der Waals forces: between the atoms themselves and atom-material interactions. For example He-4 atoms on 2D materials can potentially form a variety of exotic quantum states of matter, such as 2D supersolids and superfluids, in addition to solid phases. For the "most quantum" case of a single helium layer we discuss, from a theoretical perspective, how the effective low-energy (Bose-Hubbard) description can take advantage of the extreme sensitivity of this unique system to the interplay between the atomic (helium) and solid-state (graphene) components. Due to the extraordinary variety and tunability of 2D electronic materials, it is envisaged that a wide range of correlated atomic phases can be realized under favorable conditions. Exciting possibilities in the opposite extreme of many atomic layers forming a liquid on top of graphene are also outlined -in this case a so-called "spinodal dewetting" pattern can form at the liquid-vapor interface which reflects the presence and electronic properties of graphene underneath. Such patterns could be manipulated by choosing different atoms and materials, with potential technological applications.