Optical characterization of electron-phonon interactions at the saddle point in graphene

The role of electron-phonon interactions is experimentally and theoretically investigated near the saddle point absorption peak of graphene. The differential optical transmission spectra of multiple, non-interacting layers of graphene reveals the dominant role played by electron-acoustic phonon coupling in bandstructure renormalization. Using a Born approximation for electron-phonon coupling and experimental estimates of the dynamic phonon lattice temperature, we deduce the effective acoustic deformation potential to be $D^{\rm ac}_{\rm eff} \simeq 5$eV. This value is in accord with recent theoretical predictions but differs substantially from those obtained using electrical transport measurements.