Comment on "Charge pumping with strong spin-orbit coupling: Fermi surface breathing, Berry curvature, and higher harmonic generation"

TL;DR

This paper critiques a recent linear theory of high-order harmonic generation in spin-orbit coupled systems, emphasizing that HHG is inherently nonlinear and cannot be captured by linear models.

Contribution

It clarifies the limitations of linear theories for describing nonlinear phenomena like HHG in spin-orbit coupled materials.

Findings

Linear theory cannot describe high-order harmonic generation.

HHG is inherently a nonlinear process.

Linear models are insufficient for capturing HHG phenomena.

Abstract

In their recent work [Phys. Rev. B 109, 184409(2024)], Manchon and Pezo develop a linear (in magnetization) theory, in order to investigate high-order harmonic generation (HHG). Here, we show that such linear theory cannot describe HHG, which, by definition is a nonlinear process.