Giant Linear Dichroism Controlled by Magnetic Field in FePS_3

Magnetic-field control of fundamental optical properties is a crucial challenge in the engineering of multifunctional microdevices. Van der Waals (vdW) magnets retaining a magnetic order even in atomically thin layers, offer a promising platform for hosting exotic magneto-optical functionalities owing to their strong spin-charge coupling. Here, we demonstrate that a giant optical anisotropy can be controlled by magnetic fields in the vdW magnet FePS_3. The giant linear dichroism (∼11 is nearly fully suppressed in a wide energy range from 1.6 to 2.0 eV, following the collapse of the zigzag magnetic order above 40 T. This remarkable phenomenon can be explained as a result of symmetry changes due to the spin order, enabling minority electrons of Fe^2+ to hop in a honeycomb lattice. The modification of spin-order symmetry by external fields provides a novel route for controllable anisotropic optical micro-devices.