Tunable photon absorption and Rayleigh response in twisted bilayer graphene

We investigate the polarization-controlled absorption characteristics of twisted bilayer graphene (tBLG) subject to one and two-photon absorption. We find distinct peaks in one-photon absorption coefficient as a function of the excitation energy, corresponding to the van Hove singularities of tBLG. These peaks shift to higher energies as the rotation angle between the graphene layers is increased, even reaching the visible spectrum for higher twist angles. When subjected to two photons, introducing a twist between the two graphene layers enhances the magnitude of absorption coefficient α₂ by ~ 6 orders of magnitude, which is more pronounced in the visible region for higher θ. We explore various polarization configurations for the two photons independently and determine the condition under which α₂ becomes extremal. Additionally, we study the response of emitted photons through polarization-controlled Rayleigh scattering in tBLG. Compared to SLG, the integrated Rayleigh intensity (IRI) is strongly enhanced for small theta for parallel polarization (PP). For cross-polarization (CP), it exhibits a markedly complex behavior suggestive of strong interference effects mediated by the optical matrix elements. At small twist, the ratio R_A= IRI for PP/CP by ~1300 times viz a viz SLG. Measured as a function of the incoming energy, R_A exhibits a characteristic evolution as θ reduces, thus providing a unique fingerprint of the prevailing twist angle which would be interesting to verify experimentally.