Effect of moire superlattice reconstruction in the electronic excitation spectrum of graphene metal heterostructures
We have studied the electronic excitation spectrum in periodically rippled graphene on Ru(0 0 0 1) and flat, commensurate graphene on Ni(1 1 1) by means of high resolution electron energy loss spectroscopy and a combination of density functional theory and tight binding approaches. We show that the periodic moire superlattice originated by the lattice mismatch in graphene/Ru(0 0 0 1) induces the emergence of an extra mode, which is not present in graphene/Ni(1 1 1) Contrary to the ordinary intra band plasmon of doped graphene, the extra mode is robust in charge neutral graphene/metal contacts, having its origin in electron hole inter band transitions between van Hove singularities that emerge in the reconstructed band structure, due to the moire pattern superlattice.