The dominant phonon wavevectors q∗ probed by the 2D Raman mode of graphene are highly anisotropic and rotate with the orientation of the polarizer:analyzer direction relative to the lattice. The corresponding electronic transitions connect the electronic equibandgap contours where the product of the ingoing and outgoing optical matrix elements is strongest, showing a finite component along K−Γ that sensitively determines q∗. We revoke the notion of 'inner' and 'outer' processes. Our findings explain the splitting of the 2D mode of graphene under uniaxial tensile strain. The splitting originates from a strain-induced distortion of the phonon dispersion; changes in the electronic band structure and resonance conditions are negligeable for the 2D Raman spectrum.
@article{arxiv.1102.5317,
title = {Dominant Phonon Wavevectors and Strain-induced Splitting of the 2D Graphene Raman Mode},
author = {Rohit Narula and Nicola Bonini and Nicola Marzari and Stephanie Reich},
journal= {arXiv preprint arXiv:1102.5317},
year = {2015}
}