Raman spectra of out-of-plane phonons in bilayer graphene

The double resonance Raman spectra of the overtone of the out-of-plane tangential optical (oTO) phonon and of combinations of the LO, ZO, and ZA phonons with one another are calculated for bilayer graphene. In the case of the bilayer graphene, these Raman peaks are observed in the energy region between $1600$ and $1800$ cm^-1. We obtain results for both the fixed $q=0$ and the dispersive $q=2k$ peaks of the overtones of the oTO phonon of bilayer graphene. We calculate the double resonance Raman spectra of the combination modes coming from the LO, iTO, LA, and iTA phonons in bilayer graphene. The calculated Raman peaks are compared with the experimental results.