Nondispersive RamanDband activated by well-ordered interlayer interactions in rotationally stacked bilayer graphene

Raman measurements on monolayer graphene folded back upon itself into skewed bilayer (i.e., with interlayer rotation) presents a mechanism for Raman scattering in sp² carbons in the D-band frequency range, but without disorder. Although the parent monolayer does not exhibit a D band, the interior of the skewed bilayer produces a strong two-peak Raman feature near 1350 cm^-1; one of these peaks is nondispersive, unlike all previously observed D-band features. Within a double-resonant model of Raman scattering, these features are consistent with a skewed bilayer coupling wherein one layer imposes a weak but well-ordered perturbation on the other. The discrete Fourier structure of the rotated interlayer interaction potential explains the unusual nondispersive peak.