Nonlinear spin current of photoexcited magnons in collinear antiferromagnets

TL;DR

This paper investigates how nonlinear spin currents of photoexcited magnons are generated in collinear antiferromagnets under light irradiation, revealing mechanisms dependent on light polarization and magnon band geometry.

Contribution

It introduces the concept of nonlinear magnon spin currents driven by ac electric fields, detailing mechanisms for linearly and circularly polarized light, and models these effects in specific materials.

Findings

dc spin current from magnon spin shift current with linearly polarized light

dc spin current from spin injection current with circularly polarized light

demonstration of these effects in toy models and a multiferroic material

Abstract

We study the nonlinear magnon spin current induced by an ac electric field under light irradiation in collinear antiferromagnets with broken inversion symmetry. For linearly polarized light, we find that a dc spin current appears through ``the magnon spin shift current" mechanism, which is driven by a spin polarization generation in the two magnon creation process and has a close relationship to the geometry of magnon bands through Berry connection. For circularly polarized light, a dc spin current appears through ``the spin injection current" mechanism, which is proportional to the relaxation time of magnons and can be large when the magnon lifetime is long. We demonstrate generation of the magnon spin shift and injection currents, based on a few toy models and a realistic model for a multiferroic material M$_2$Mo$_3$O$_8$.