Comment on "Raman spectra of misoriented bilayer graphene"

TL;DR

This paper challenges a recent claim about the excitation energy dependence of the 2D band blueshift in misoriented bilayer graphene, providing additional experimental evidence supporting a different explanation based on Fermi velocity reduction.

Contribution

The authors present new experimental data showing weak excitation energy dependence of the 2D band blueshift, reaffirming their Fermi velocity reduction explanation for folded graphene.

Findings

Blueshift of 2D band is weakly dependent on excitation energy.

Additional experimental results support Fermi velocity reduction as the cause.

Contradicts previous claims of strong excitation energy dependence.

Abstract

In a recent paper [Phys. Rev. B 78, 113407 (2008)], Poncharal et al. studied the Raman spectra of misoriented bilayer graphene. They found that the blueshift of 2D band of misoriented graphene relative to that of single layer graphene shows a strong dependence on the excitation laser energy. The blueshift increases with decreasing excitation energy. This finding contradicts our explanation of reduction of Fermi velocity of folded/misoriented graphene [Ni et al. Phys. Rev. B 77, 235403 (2008)]. In this comment, we present more experimental results from our group as well as from others to show that the blueshift is indeed only weakly dependent on excitation energy. We therefore suggest that our explanation of 2D blushift of folded graphene due to reduction of Fermi velocity is still valid.