Fermi energy dependence of first- and second-order Raman spectra in graphene: Kohn anomaly and quantum interference effect

Intensity of the first- and the second-order Raman spectra are calculated as a function of the Fermi energy. We show that the Kohn anomaly effect, i.e., phonon frequency renormalization, in the first-order Raman spectra originates from the phonon renormalization by the interband electron-hole excitation, whereas in the second-order Raman spectra, a competition between the interband and intraband electron-hole excitations takes place. By this calculation, we confirm the presence of different dispersive behaviors of the Raman peak frequency as a function of the Fermi energy for the first- and the second-order Raman spectra, as observed in experiments. Moreover, the calculated results of the Raman intensity sensitively depend on the Fermi energy for both the first- and the second-order Raman spectra. These results thus also show the importance of quantum interference effect phenomena.Comment: 9 pages, 10 figure

Breit-Wigner-Fano lineshapes in Raman spectra of graphene

Excitation of electron-hole pairs in the vicinity of the Dirac cone by the Coulomb interaction gives rise to an asymmetric Breit-Wigner-Fano lineshape in the phonon Raman spectra in graphene. This asymmetric lineshape appears due to the interference effect between the phonon spectra and the electron-hole pair excitation spectra. The calculated Breit-Wigner-Fano asymmetric factor 1/qBWF as a function of the Fermi energy shows a V-shaped curve with a minimum value at the charge neutrality point and gives good agreement with the experimental result.Comment: 15 pages, 4 figure