Highly anisotropic microwave third-harmonic generation due to mobile carriers in a graphene superlattice

We use a microscopic semiclassical approach based on the Boltzmann transport equation to explore the microwave third-harmonic generation (THG) due to mobile carriers in a one-dimensional graphene superlattice on a SiC substrate. As a model of the periodic potential of the superlattice, we adopt the piecewise constant Kronig–Penney potential. For the case of microwave radiation normally incident on the graphene superlattice, we calculate the THG conductivity of the superlattice both in the direction of its periodicity and in the perpendicular direction, and then evaluate the corresponding output THG powers from the superlattice in the reflected direction. The results obtained testify to a very strong dependence of this power on the polarization direction of the incident radiation (along or across the superlattice period) and, in addition, show that the superlattice potential applied to graphene can significantly enhance the microwave THG in graphene, which offers additional technological potentials for the design of graphene-based microwave frequency multipliers and up-converters needed for high data rate communication links.