Superlattice Dirac points and space-dependent Fermi velocity in a corrugated graphene monolayer

Recent studies show that periodic potentials can generate superlattice Dirac points at energies $\ifmmode\pm\else\textpm\fi{}\ensuremath{\hbar}{\ensuremath{\nu}}_{\mathrm{F}}|\mathbf{G}|/2$ in graphene (where $\ensuremath{\hbar}$ is the reduced Planck constant, ${\ensuremath{\nu}}_{\mathrm{F}}$ 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 quasiperiodic ripples of nanometer wavelength in the corrugated graphene give rise to weak one-dimensional 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 demonstrate that the space-dependent superlattice Dirac points are 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.