Strain-dependent Raman analysis of the G* band in graphene

Compared with the well-established theory for other graphene Raman bands, the origin of the ${\mathrm{G}}^*$ band at $\ensuremath{\sim}2450\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ remains unclear. A major debate lies at whether it should be assigned solely to the combined $q\ensuremath{\ne}0$ in-plane (i) transverse-optical (TO) and longitudinal-acoustic (LA) phonon modes, or to such a combination with additional $q=0 i\mathrm{TO}$ phonon overtones. A strain-dependent Raman analysis shows that during uniaxial strain this band exhibits only frequency redshift but no line shape changes. It is well interpreted by first-principles calculations, and thereby unambiguously identifies the origin of the ${\mathrm{G}}^*$ band as the $q\ensuremath{\ne}0 i\mathrm{TO}$ and LA phonon combination.