  We demonstrate that surface relaxation, which is insignificant in trilayer
graphene, starts to manifest in Bernal-stacked tetralayer graphene.
Bernal-stacked few-layer graphene has been investigated by analyzing its Landau
level spectra through quantum capacitance measurements. We find that in
trilayer graphene, the interlayer interaction parameters were similar to that
of graphite. However, in tetralayer graphene, the hopping parameters between
the bulk and surface bilayers are quite different. This shows a direct evidence
for the surface relaxation phenomena. In spite of the fact that the Van der
Waals interaction between the carbon layers is thought to be insignificant, we
suggest that the interlayer interaction is an important factor in explaining
the observed results and the symmetry-breaking effects in graphene sublattice
are not negligible.
