Anisotropic polarization due to electron-phonon interactions in graphene

Polarization plays an important role in the Raman spectroscopy. We study, in graphene, anisotropic polarization due to electronphonon coupling (EPC). The numerical results show that the anisotropy is obvious even when the wave vector is in the range of the Raman experiment. The analytical expression is deduced from the structure factor, which indicates the crucial origin of the anisotropy. We also find that, as the phonon energy increases the polarization is clearly weakened due to the screen effect of EPC, but the anisotropy totally remains.