Photocontrol of magnetic structure in an itinerant magnet

TL;DR

This study demonstrates that intense light can induce an antiferromagnetic order in an itinerant magnet by destabilizing the ferromagnetic state through nonequilibrium electron dynamics and Floquet state analysis.

Contribution

It introduces a mechanism for photoinduced antiferromagnetic transition in an itinerant magnet using Floquet Green function formalism and magnon spectrum analysis.

Findings

Intense light causes magnon softening at $(\pi,\pi)$, indicating AFM instability.

Photoinduced AFM state is driven by nonequilibrium electron distribution and low-energy excitations.

Optical spectra reveal signatures of the photoinduced AFM order through interband and Floquet sidepeak features.

Abstract

We study the photoinduced magnetic transition in an itinerant magnet described by the double-exchange model, in which conduction electrons couple with localized spins through the ferromagnetic (FM) Hund coupling. It is shown that intense light applied to the FM ground state induces an antiferromagnetic (AFM) order, in contrast to the AFM-to-FM transition due to the photocarrier injection. In particular, we focus on the mechanism for instability of the FM structure by the light irradiation. The magnon spectrum in the Floquet state is formulated on the basis of the pertrubative expansion of the Floquet Green function. The magnon dispersion shows softening at momentum $(\pi,\pi)$ in the square lattice with increasing the light amplitude, implying photoinduced AFM instability. This result is mainly attributed to a nonequilibrium electron distribution, which promotes low-energy Stoner excitations. The transient optical conductivity spectra characterized by interband excitations and Floquet sidepeaks are available to identify the photoinduced AFM state.