Abstract
We report on strong coupling of the charge-carrier plasmon in graphene with the surface-optical phonon of the underlying SiC(0001) substrate with low-electron concentration in the long-wavelength limit . Energy-dependent energy-loss spectra give clear evidence of two coupled phonon-plasmon modes separated by a gap between and , the transverse-optical-phonon mode, in particular, for higher primary electron energies . A simplified model based on dielectric theory is able to simulate our energy-loss spectra as well as the dispersion of the two coupled phonon-plasmon modes . In contrast, Liu and Willis [Phys. Rev. B 81, 081406(R) (2010)] postulate in their recent publication no gap and a discontinuous dispersion curve with a one-peak structure from their energy-loss data.
- Received 6 August 2010
DOI:https://doi.org/10.1103/PhysRevB.82.201413
©2010 American Physical Society