Light-assisted spontaneous birefringence and magnetic-domain formation in a suspension of gyrotropic nanoparticles

Abstract

We show that linearly polarized light in a suspension of gyrotropic nanoparticles can experience modulation instability, which leads to spatial separation of right- and left-circularly polarized waves. Such a separation preserves zero full angular momentum of the electromagnetic field; thus, the time-reversal symmetry is broken only locally. Eventually, this instability results in the formation of the lattice of spatial solitons with alternating right and left circular polarization. As magnetic moments of nanoparticles tend to reorient parallel to the wave vector in circularly polarized light, every spatial soliton captures a static magnetic field directed along or opposite to the wave vector depending on the direction of the field angular momentum; therefore, the soliton lattice altogether looks like an array of magnetic domains with antiferromagnetic ordering.