Effect of moir\'e superlattice reconstruction in the electronic   excitation spectrum of graphene-metal heterostructures
  We have studied the electronic excitation spectrum in periodically rippled graphene on Ru(0001) and flat, commensurate graphene on Ni(111) 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 moir\'e superlattice originated by the lattice mismatch in graphene/Ru(0001) induces the emergence of an extra mode, which is not present in graphene/Ni(111). 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 moir\'e pattern superlattice. 
Antonio Politano, Guus J. Slotman, Rafael Rold\'an, Gennaro Chiarello,   Davide Campi, Mikhail I. Katsnelson, Shengjun Yuan
cond-mat.mes-hall