Fano resonances and their strong doping dependence are observed in Raman scattering of single-layer graphene (SLG). As the Fermi level is varied by a back-gate bias, the Raman G band of SLG exhibits an asymmetric line shape near the charge neutrality point as a manifestation of a Fano resonance, whereas the line shape is symmetric when the graphene sample is electron or hole doped. However, the G band of bilayer graphene (BLG) does not exhibit any Fano resonance regardless of doping. The observed Fano resonance can be interpreted as interferences between the phonon and excitonic many-body spectra in SLG. The absence of a Fano resonance in the Raman G band of BLG can be explained in the same framework since excitonic interactions are not expected in BLG.
@article{arxiv.1305.5589,
title = {Fano resonance in Raman scattering of graphene},
author = {Duhee Yoon and Dongchan Jeong and Hu-Jong Lee and Riichiro Saito and Young-Woo Son and Hyun Cheol Lee and Hyeonsik Cheong},
journal= {arXiv preprint arXiv:1305.5589},
year = {2013}
}