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.
11 Jan 2017
Volume: 4 Issue: 2 Pages: 021001