Strong terahertz magneto-optical phenomena based on quasi-bound states in the continuum and Fano resonances

We propose new ways to produce strong terahertz (THz) magneto-optical phenomena from monolayer graphene based on bound states in the continuum (BICs) and Fano resonances. The BICs and Fano resonances of radiation modes in the monolayer graphene are realized by designing the photonic crystal slab-graphene-slab structure. Based on them, the magnetic circular dichroism near 100% has been achieved. Importantly, such magneto-optical phenomena can be modulated in intensity and frequency using only electrostatic doping at a fixed magnetic field. Comparing two ways to produce magneto-optical phenomena, it is found that the way based on BICs exhibits some advantages such as good electrical tenability due to narrower resonance width, higher conversion efficiency and more stability with the change of incident angle. These phenomena can appear in a broad THz range by designing the nanostructures, which are very beneficial to polarization conversion and optoelectronic devices.