Charge density wave state of monolayers in graphite intercalation compounds

The electronic structure of a graphite monolayer with electron count corresponding to the graphite intercalation compound (GIC), described by the extended Hubbard Hamiltonian, is studied in the unrestricted Hartree-Fock approximation. We also interpret the data on observed STM images of graphite intercalation compounds. The well-known (and puzzling) pattern of graphite STM images with only three of the six atoms of each carbon hexagon visible is tentatively explained by the formation of a charge density wave (CDW) state of the surface graphite monolayer, which is an intrinsic feature of its electronic structure, rather than invoking well-known attributions of the observed effect to structural differences between the sites and/or to interactions external to the monolayer. A tentative, purely electronic, explanation for the Moire patterns is proposed as well.