High harmonic generation in undoped graphene: Interplay of inter- and intraband dynamics

TL;DR

This paper develops a density matrix approach to study high harmonic generation in undoped graphene, revealing strong nonlinear responses due to inter- and intraband dynamics at terahertz frequencies.

Contribution

It introduces a novel formalism combining inter- and intraband effects to accurately predict harmonic generation in graphene.

Findings

Third harmonic amplitude reaches 32% of the fundamental at 100 V/cm.

Up to the seventh harmonic and beyond are generated.

Strong harmonic signals are observed at moderate field amplitudes.

Abstract

We develop a density matrix formalism in the length gauge to calculate the nonlinear response of intrinsic monolayer graphene at terahertz frequencies. Employing a tight-binding model, we find that the interplay of the interband and intraband dynamics leads to strong harmonic generation at moderate field amplitudes. In particular, we find that at low temperature, the reflected field of undoped suspended graphene exhibits a third harmonic amplitude that is 32% of the fundamental for an incident field of 100 V/cm. Moreover, we find that up to the seventh harmonic and beyond are generated.