Fano resonance in Raman scattering of graphene

Abstract

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.

Resonance Raman Spectrum of Doped Epitaxial Graphene at the Lifshitz Transition

“…The Fano lineshape of the G band is more pronounced for larger doping levels 26 and for a higher layer number. 27 The most pronounced Fano asymmetries are obtained in stage 1…”

“…For graphene, the first-order Raman spectrum due to zone-center optical phonons with in-plane polarization (the G band) shows an asymmetric Fano lineshape if graphene is doped by field effect gating 26 or alkali metal doping 27 . This lineshape is reproduced theoretically by considering the interference between a discrete transition (phonon) to a continuum (excitation of electron-hole pairs) which is known as electronic Raman spectra (ERS).…”

Excitation energy dependence of Raman spectra of few-layer WS2

“…It should be noted that the lowest shear modes have pronounced asymmetric line shapes that are indicative of Fano resonance, which is characterized by the Breit-Wigner-Fano (BWF) line shape [55][56][57],…”

Breit-Wigner-Fano line shapes in Raman spectra of graphene

“…The asymmetric BWF line shapes in graphite-related systems are normally found in the Raman shift around 1600 cm −1 , known as the G modes, which correspond to two zone-center (q = 0) phonon modes, namely the in-plane tangential optic (iTO) and longitudinal optic (LO) modes. In graphene, the BWF asymmetry of the G band is observed using gatemodulated Raman spectroscopy [9]. The asymmetric factor (1/q BWF ) has a value around −0.06 or one-order of magnitude smaller than those found in m-SWNTs (1/q BWF ≈ −0.4) [7] and in GICs (1/q BWF ≈ −0.5) [6].…”