Effect of moiré 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 moiré 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 moiré pattern superlattice.The support by the Netherlands National Computing Facilities foundation (NCF) are acknowledged. SY and MIK thank financial support from the European Research Council Advanced Grant program (contract 338957). The research has also received funding from the European Union Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship. RR acknowledges financial support from MINECO (Spain) through grant FIS2014-58445-JIN.Peer reviewe