Magnon harmonic generation in antiferromagnets: Dynamical symmetry enriched by symmetry breaking

TL;DR

This paper explores how intense THz lasers induce nonlinear magnon harmonic generation in antiferromagnets, revealing how magnetic order and symmetry breaking influence the spectra.

Contribution

It provides a theoretical and numerical analysis of magnon harmonic generation in various antiferromagnetic phases, highlighting the role of dynamical symmetries and selection rules.

Findings

Harmonic spectra are affected by magnetic order and phase transitions.

Dynamical symmetries determine selection rules for harmonic generation.

Magnon harmonic spectra reveal information about symmetry breaking.

Abstract

In recent years, techniques of intense THz laser have enabled us to experimentally observe nonlinear spin dynamics in antiferromagnets since the elementary excitations such as magnons reside on a THz to GHz range in antiferromagnets and THz laser thus can directly excite them. We numerically and theoretically investigate THz-laser or GHz-wave driven harmonic generations in typical ordered phases of antiferromagnets: N\'eel, canted and weak ferromagnetic phases. The radiation waves (harmonic generations) are created by the incident-wave driven magnon dynamics. We point out that magnetic orders and phase transitions can change the spectra of harmonic generations, differently from those of metallic, semiconductor, or atomic-gas systems without (spontaneous) symmetry breakings. We consider both the magnon harmonic generation driven by standard single-color laser and that by two-color laser in the antiferromagnets, and find several dynamical symmetries and the corresponding selection rules of the harmonic generations. These results indicate that the magnon harmonic generation spectra provide new information about symmetry or symmetry breaking of antiferromagnets.