Optical Radiation Trapping by Current in Gyrotropic Liquid Metacrystals

It is shown that direct electric current passing through a suspension of gyrotropic nanoparticles with residual magnetization (gyrotropic liquid metacrystal) forms a unidirectional waveguide for optical radiation so that trapped light can propagate only in the direction opposite to the direction of current. The localization of electromagnetic radiation is associated with the emergence of nonuniform gyrotropy of the medium as a result of reorientation of magnetic nanoparticles in the nonuniform magnetic field of the current. By way of examples, we consider the trapping of the radiation by a plane current sheet and by a cylindrical current-carrying filament. The dispersion equations of trapped modes are derived and analyzed. The analogy with topologically protected edge photon states is considered.