Light-induced magnetization driven by interorbital charge motion in a spin-orbit assisted Mott insulator alpha-RuCl3

TL;DR

This study demonstrates that circularly polarized light can induce ultrafast magnetization in alpha-RuCl3 by driving interorbital charge motion, revealing a new mechanism for light-controlled magnetic states in spin-orbit Mott insulators.

Contribution

It uncovers a novel ultrafast magnetization mechanism driven by interorbital charge motion in a spin-orbit Mott insulator, supported by femtosecond measurements and quantum analysis.

Findings

Ultrafast 6-fs photo-carrier dynamics observed.

Magnetization induced by circularly polarized light via interorbital charge motion.

Magnetization effect is suppressed in the antiferromagnetic phase.

Abstract

In a honeycomb-lattice spin-orbit assisted Mott insulator {\alpha}-RuCl3, an ultrafast magnetization is induced by circularly polarized excitation below the Mott gap. Photo-carriers play an important role, which are generated by turning down the synergy of the on-site Coulomb interaction and the spin-orbit interaction realizing the insulator state. An ultrafast 6- fs measurement of photo-carrier dynamics and a quantum mechanical analysis clarify the mechanism, according to which the magnetization emerges from a coherent charge motion between different t2g orbitals (dyz-dxz-dxy) of Ru3+ ions. This ultrafast magnetization is weakened in the antiferromagnetic (AF) phase, which is opposite to the general tendency that the inverse Faraday effect is larger in AF compounds than in paramagnetic ones. This temperature dependence indicates that the interorbital charge motion is affected by pseudo-spin rotational symmetry breaking in the AF phase.