  We report on microscopic measurements of the low-energy electronic structures
both at zigzag and armchair edges of bilayer graphene using scanning tunneling
microscopy and spectroscopy (STM and STS). We have found that, both in the
absence and in the presence of a magnetic field, an almost zero-energy peak in
density of states was localized at zigzag edges, as expected for the surface
states at zigzag edges of bilayer graphene. In the quantum Hall regime, we have
observed clearly Landau levels bending away from the charge neutrality point
near both the zigzag and armchair edges. Such a result is a direct evidence for
the evolution of Landau levels into the quantum Hall edge states in graphene
bilayers. Our experiment indicates that it is possible to explore rich quantum
Hall physics in graphene systems using STM and STS.
