Terahertz-induced high-order harmonic generation and nonlinear charge transport in graphene

TL;DR

This paper theoretically investigates how terahertz pulses induce high-order harmonic generation and nonlinear charge transport in graphene, revealing the importance of nonequilibrium electron dynamics in these phenomena.

Contribution

It introduces a microscopic model using the quantum master equation to accurately describe THz-induced effects in graphene, comparing dynamical and quasi-static approaches.

Findings

THz-induced HHG originates from reduced effective conductivity due to electron displacement.

Nonequilibrium steady-state approximation effectively models electron dynamics in graphene.

The nonequilibrium nature significantly influences nonlinear optical and transport phenomena.

Abstract

We theoretically study the THz-induced high-order harmonic generation (HHG) and nonlinear electric transport in graphene based on the quantum master equation with the relaxation time approximation. To obtain microscopic insight into the phenomena, we compare the results of the fully dynamical calculations with those under a quasi-static approximation, where the electronic system is approximated as a nonequilibrium steady state. As a result, we find that the THz-induced electron dynamics in graphene can be accurately modeled with the nonequilibrium steady-state at each instance. The population distribution analysis further clarifies that the THz-induced HHG in graphene originates from the reduction of effective conductivity due to a large displacement of electrons in the Brillouin zone. By comparing the present nonequilibrium picture with a thermodynamic picture, we explore the role of the nonequilibrium nature of electron dynamics on the extremely nonlinear optical and transport phenomena in graphene.