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

In a honeycomb-lattice spin-orbit assisted Mott insulator alpha-RuCl3, ultrafast magnetization is induced by circularly polarized excitation below the Mott gap. Photocarriers play an important role, which are generated by turning down the synergy of the onsite Coulomb interaction and the spin-orbit interaction realizing the insulator state. An ultrafast 6 fs measurement of photocarrier dynamics and a quantum mechanical analysis clarify the mechanism, according to which the magnetization emerges from a coherent charge motion between different t(2g) orbitals (d(yz)-d(xz)-d(xy)) of Ru3+ ions. This ultrafast magnetization is weakened in the antiferromagnetic (AFM) phase, which is opposite to the general tendency that the inverse Faraday effect is larger in AFM compounds than in paramagnetic ones. This temperature dependence indicates that the interorbital charge motion is affected by pseudospin rotational symmetry breaking in the AFM phase.