Many-Body Effects in Third Harmonic Generation of Graphene

TL;DR

This paper uses a many-body approach to analyze how interactions affect third harmonic generation in graphene, revealing incoherent features and limitations of phenomenological models in the terahertz regime.

Contribution

It provides a systematic many-body analysis of THG in graphene, highlighting interaction-driven incoherent features and the conditions where phenomenological models fail.

Findings

Interaction induces incoherent features at four- and five-photon frequencies.

Purely intraband response aligns with phenomenological models despite complex interactions.

Many-body effects limit the applicability of simplified phenomenological descriptions.

Abstract

The low-energy (intraband) range of the third harmonic generation of graphene in the terahertz regime is governed by the damping terms induced by the interactions. A controlled many-body description of the scattering processes is thus a compelling and desirable requirement. In this paper, using a Kadanoff-Baym approach, we systematically investigate the impact of many-body interaction on the third-harmonic generation (THG) of graphene, taking elastic impurity scattering as a benchmark example. We predict the onset in the mixed inter-intraband regime of novel incoherent features driven by the interaction at four- and five-photon transition frequencies in the third-harmonic optical conductivity with a spectral weight proportional to the scattering rate.We show also that, in spite of the complex many-body physics, the purely intraband term governing the limit $\omega \to 0$ resembles the constraints of the phenomenological model. We ascribe this agreement to the fulfilling of the conservation laws enforced by the conserving approach. The overlap with novel incoherent features and the impact of many-body driven multi-photon vertex couplings limit however severely the validity of phenomenological description.