Using scanning tunneling microscopy and spectroscopy, we have studied the
local density of states (LDOS) of graphene over step edges in boron nitride.
Long wavelength oscillations in the LDOS are observed with maxima parallel to
the step edge. Their wavelength and amplitude are controlled by the energy of
the quasiparticles allowing a direct probe of the graphene dispersion relation.
We also observe a faster decay of the LDOS oscillations away from the step edge
than in conventional metals. This is due to the chiral nature of the Dirac
fermions in graphene.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
