The effects of microscopic scattering on terahertz third harmonic generation in monolayer graphene

TL;DR

This paper models how microscopic scattering processes affect terahertz third harmonic generation in monolayer graphene, revealing that scattering significantly influences the nonlinear response and aligning simulations with experimental observations.

Contribution

It introduces a microscopic model including phonon and impurity scattering to analyze third harmonic generation in graphene, highlighting the impact of scattering on nonlinear optical responses.

Findings

Scattering greatly affects third harmonic generation in graphene.

Microscopic models show lower harmonic fields than semiclassical approximations.

Results qualitatively agree with recent experimental data.

Abstract

Due to its linear dispersion, monolayer graphene is expected to generate a third harmonic response at terahertz frequencies. There have been a variety of different models of this effect and recently it has been experimentally observed. However, there is still considerable uncertainty as to the role of scattering on harmonic generation in graphene. In this work, we model third-harmonic generation in doped monolayer graphene at THz frequencies by employing a nearest-neighbour tight-binding model in the length gauge. We include optical phonon and neutral impurity scattering at the microscopic level, and examine the effects of scattering on the third harmonic response. We also compare the results of a phenomenological semiclassical theory, using a field-dependent scattering time extracted from the simulation, and find a significantly lower third harmonic field than that found from the microscopic model. This demonstrates that third-harmonic generation is much more sensitive to the nature of the scattering than is the linear response. We also compare the results of our full simulation to recent experimental results and find qualitative agreement.