Polarization-dependent magnetic properties of periodically driven $\alpha$-RuCl$_{3}$

TL;DR

This paper investigates how linearly polarized light can modify magnetic interactions and states in a driven $ ext{RuCl}_3$ system, revealing potential control over magnetic phases via light polarization.

Contribution

It derives an effective Hamiltonian for a driven spin-orbit coupled Mott insulator and shows how linearly polarized light can induce bond anisotropy and alter magnetic state stability.

Findings

Linearly polarized light changes exchange interaction magnitudes and signs.

Light polarization can transform honeycomb spins into zigzag or chain-like states.

Circularly polarized light does not significantly alter magnetic state stability.

Abstract

We study magnetic properties of a periodically driven Mott insulator with strong spin-orbit coupling and show some properties characteristic of linearly polarized light. We consider a $t_{2g}$-orbital Hubbard model driven by circularly or linearly polarized light with strong spin-orbit coupling and derive its effective Hamiltonian in the strong-interaction limit for a high-frequency case. We show that linearly polarized light can change not only the magnitudes and signs of the exchange interactions, but also their bond anisotropy even without the bond-anisotropic hopping integrals. Because of this property, the honeycomb-network spin system could be transformed into weakly coupled zigzag or step spin chains for the light field polarized along the $b$- or $a$-axis, respectively. Then, analyzing how the light fields affect several magnetic states in a mean-field approximation, we show that linearly polarized light can change the relative stability of the competing magnetic states, whereas such a change is absent for circularly polarized light. We also analyze the effects of both the bond anisotropy of nearest-neighbor hopping integrals and a third-neighbor hopping integral on the magnetic states and show that the results obtained in a simple model, in which the bond-averaged nearest-neighbor hopping integrals are considered, remain qualitatively unchanged except for the stability of zigzag states in the non-driven case and the degeneracy lifting of the zigzag or stripy states.