Nonlinear Response of Nanostructured Graphene to Circularly Polarized Light

Using the tight-binding description of graphene and the time-dependent density matrix approach, we theoretically address the nonlinear response of plasmonic graphene nanostructures to the circularly polarized light. The intensity and polarization of emitted harmonics depend on the symmetry of the system and can be analyzed by applying Neumann's principle. We find that for the nanoflakes comprising thousands of carbon atoms, it is the symmetry of the carbon atom arrangement on the atomic scale that determines the nonlinear response. Therefore, it might be very different from the nonlinear response predicted using the macroscopic geometry. For the compound systems made of several nanoflakes, we reveal the role of the near-field interactions in intensity and circular polarization states of emitted harmonics. Finally, we show that symmetry break by, e.g., lattice defects strongly affects the nonlinear response of graphene nanoflakes to the circularly polarized light. Our work extends the theoretical studies of the nonlinear optical properties of graphene nanomaterials toward spin-carrying light beams.