We report multiphonon Raman scattering in graphene samples. Higher order
combination modes involving 3 phonons and 4 phonons are observed in
single-layer (SLG), bi-layer (BLG), and few layer (FLG) graphene samples
prepared by mechanical exfoliation. The intensity of the higher order phonon
modes (relative to the G peak) is highest in SLG and decreases with increasing
layers. In addition, all higher order modes are observed to upshift in
frequency almost linearly with increasing graphene layers, betraying the
underlying interlayer van der Waals interactions.Comment: Accepted for publication in Phys. Rev.
