Signature of electronic excitations in the Raman spectrum of graphene

Inelastic light scattering from Dirac-type electrons in graphene is shown to be dominated by the generation of the inter-band electronic modes which are odd in terms of time-inversion symmetry and belong to the irreducible representation A$_2$ of the point group C$_{6v}$ of the honeycomb crystal. At high magnetic fields, these electron-hole excitations appear as peculiar $n^- \to n^+$ inter-Landau-level modes with energies $\omega_n=2\sqrt{2n} \hbar v/\lambda_B$ and characteristically crossed polarisation of in/out photons.