Raman scattering study of the phonon dispersion in twisted bilayer graphene

Bilayer graphene with a twist angle theta between the layers generates a superlattice structure known as a Moir, pattern. This superlattice provides a theta-dependent q wavevector that activates phonons in the interior of the Brillouin zone. Here we show that this superlattice-induced Raman scattering can be used to probe the phonon dispersion in twisted bilayer graphene (tBLG). The effect reported here is different from the widely studied double-resonance in graphene-related materials in many aspects, and despite the absence of stacking order in tBLG, layer breathing vibrations (namely ZO' phonons) are observed.