Interaction of magneto-excitons with phonons in graphene and graphite

We study the Landau levels of graphite and single layer graphene by measurements of the magneto-phonon resonance effect in which there is coupling between the inter-Landau level magneto-exciton with the long wavelength optical phonon (G band). In graphite the G band displays a rich line shape evolution as the magnetic field is finely tuned between 5 and 7 Tesla. These observations indicate that the G band is resonantly coupled to the magneto-excitions at these fields. In the interpretation we postulate that the anticrossing of the phonon band with the inter-Landau level transitions results in a mode-splitting at around 6.2 T. The evolution of the energy and spectral weight of the two coupled modes indicates that the phonon is a probe of the unique structure of Landau levels in graphene-related materials. In an as-prepared single-layer graphene, much smaller changes are observed for fields reaching as high as 12 Tesla.