Dominant Role of Two-Photon Vertex in Nonlinear Response of Dirac Materials

TL;DR

This paper develops a comprehensive theory for the nonlinear dc response of Dirac materials, emphasizing the dominant role of a self-generated two-photon vertex that influences the response even with weak interactions.

Contribution

It introduces a novel many-body mechanism involving a self-generated two-photon vertex that governs nonlinear responses in Dirac systems, absent at the bare level.

Findings

Two-photon vertex dominates nonlinear response

Frequency and field dependence of scattering rates are crucial

Predicted observable effects in Dirac materials

Abstract

Using a conserving Baym-Kadanoff approach, we present a fully compelling theory of nonlinear dc response of a Dirac system to electric fields in the presence of disorder scattering. We show that the nonlinear terms are strikingly ruled by the appearance of a dominant two-photon vertex which is absent at the bare level and finite even in the weak-coupling limit. Such two-photon vertex self-generation highlights the crucial role of the frequency and field dependence of the scattering rates in the nonlinear regime. Our study reveals a novel many-body mechanism in the nonlinear response of Dirac materials whose effects are predicted to be observable.