Theoretical study of the THz induced high-order harmonic generation and nonlinear transport in graphene

We theoretically study the microscopic mechanism of THz-induced HHG in graphene with the quantum master equation. By changing chemical potential, the enhancement of emitted harmonics is observed, consistently with the recent experimental observation. We find that the THz-induced electron dynamics are well described by a nonequilibrium steady-state at each instance under quasi-static approximation. Additionally, we compared our nonequilibrium model with the previously developed thermodynamic model and clarified that the nonequilibrium nature is indispensable to properly describe the THz-induced HHG and nonlinear charge transport in graphene in the strong field regime. Furthermore, we discuss a method to enhance or suppress the MIR laser-induced HHG in graphene coupled with few-cycle THz pulses, opening paths toward achieving ultrafast control of charge transport by light through non-equilibrium and nonlinear electron dynamics in matter.