LAUSR

We present a theoretical description of the third-order response induced by an elliptically-polarized terahertz beam normally-incident on intrinsic and extrinsic metallic armchair graphene nanoribbons. Our results show that using a straightforward experimental setup, it should be possible to observe novel polarization-dependent nonlinearities at low excitation field strengths of the order of ${\text{10}}^4 \; \text{V/m}$. At low temperatures the Kerr nonlinearities in extrinsic nanoribbons persist to significantly higher excitation frequencies than they do for linear polarizations, and at room temperatures, the third-harmonic nonlinearities are enhanced by $2\hbox{--}3$ orders of magnitude. Finally, the Fermi-level and temperature dependence of the nonlinear response is characterized.