Evidence for Superlattice Dirac Points and Space-dependent Fermi Velocity in Corrugated Graphene Monolayer

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to reveal how nanometer-scale ripples in corrugated graphene induce superlattice Dirac points and cause the Fermi velocity to vary spatially due to local strain and electron interactions.

Contribution

It provides experimental evidence linking nanoscale ripples in graphene to superlattice Dirac points and space-dependent Fermi velocity, highlighting the effects of local strain and electron interactions.

Findings

Superlattice Dirac points arise from quasi-periodic ripples.

The Dirac point position varies across the sample.

Fermi velocity is spatially dependent due to local effects.

Abstract

Recent studies show that periodic potentials can generate superlattice Dirac points at energies in graphene (is the Fermi velocity of graphene and G is the reciprocal superlattice vector). Here, we perform scanning tunneling microscopy and spectroscopy studies of a corrugated graphene monolayer on Rh foil. We show that the quasi-periodic ripples of nanometer wavelength in the corrugated graphene give rise to weak one-dimensional (1D) electronic potentials and thereby lead to the emergence of the superlattice Dirac points. The position of the superlattice Dirac point is space-dependent and shows a wide distribution of values. We demonstrated that the space-dependent superlattice Dirac points is closely related to the space-dependent Fermi velocity, which may arise from the effect of the local strain and the strong electron-electron interaction in the corrugated graphene.