Fig. 5
From: Broken symmetries, non-reciprocity, and multiferroicity
Optical diode effect in the polar ferromagnet FeZnMo3O8. The ferromagnetic ordering temperature T C = 14 K. Optical diode effect was observed in the geometry shown in the top panel (corresponding to Fig. 3d), where the light propagates along and opposite to the toroidal vector P × M. The polarization vector P is along the crystallographic c axis. The magnetic direction M is set by applying an external magnetic field perpendicular to P. a Magnetic field dependence of the optical diode effect. No effect is observed in zero field. The absorption resonance at 1.27 THz in zero field is due to a spin excitation across the anisotropy gap. The spin resonance frequency increases with the magnetic field. At the same time, the resonant absorption is almost entirely suppressed for one direction of the magnetic field and is greatly enhanced for the opposite magnetic field direction. By symmetry, this is equivalent to non-reciprocal light propagation. Solid lines show the positive magnetic field, open symbols show the negative magnetic field. b Temperature dependence of the optical diode effect, which remains strong even far above T C . Figures are adapted with permission from ref. 37, copyright 2018 American Physical Society
