Probing strain-induced changes in the electronic structure of graphene by Raman spectroscopy

Two-phonon Raman scattering in graphitic materials provides a distinctive approach to probing the material's electronic structure through the spectroscopy of phonons. This sensitivity arises from the role of resonant electronic transitions in two-phonon Raman scattering process. The 2D mode, for instance, is known to display a strong variation with thickness in few-layer graphene. This behavior is a consequence the change of the electronic structure of the material with thickness. Here we report studies of Raman scattering of the 2D mode of single-layer graphene under uniaxial stress and the implications of these measurements for the electronic structure of anisotropically strained graphene. Under anisotropic strain, two types of modification of the low-energy electronic structure of graphene are present: a deformation of the Dirac cone and its displacement away from the K point. By analyzing the 2D Raman spectrum for excitation at different photon energies, we have identified both effects. The direct influence of strain on the 2D phonons will also be discussed.