Effect of moir\'e superlattice reconstruction in the electronic excitation spectrum of graphene-metal heterostructures

TL;DR

This study investigates how moiré superlattice patterns in graphene-metal heterostructures affect their electronic excitation spectra, revealing an extra mode in rippled graphene on Ru(0001) caused by inter-band transitions.

Contribution

It demonstrates the emergence of an additional excitation mode in rippled graphene due to moiré superlattice effects, a phenomenon not observed in flat graphene on Ni(111).

Findings

Extra mode appears in rippled graphene/Ru(0001)

Mode is due to inter-band transitions at van Hove singularities

Mode persists in charge-neutral conditions

Abstract

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.