Theory of the strongly nonlinear electrodynamic response of graphene: A hot electron model

An electrodynamic response of graphene to a strong electromagnetic radiation is considered. A hot electron model (HEM) is introduced and a corresponding system of nonlinear equations is formulated. Solutions of this system are found and discussed in detail for intrinsic and doped graphene: the hot electron temperature, non-equilibrium electron and holes densities, absorption coefficient and other physical quantities are calculated as functions of the incident wave frequency $\omega$ and intensity $I$, of the equilibrium chemical potential $\mu_0$ and temperature $T_0$, scattering parameters, as well as of the ratio $\tau_\epsilon/\tau_{\rm rec}$ of the intra-band energy relaxation time $\tau_\epsilon$ to the recombination time $\tau_{\rm rec}$. The influence of the radiation intensity on the absorption coefficient $A$ at low ($\hbar\omega\lesssim 2|\mu_0|$, $dA/dI>0$) and high ($\hbar\omega\gtrsim 2|\mu_0|$, $dA/dI<0$) frequencies is studied. The results are shown to be in good agreement with recent experimental data.