Enhanced magnetic circular dichroism by subradiant plasmonic mode in symmetric graphene oligomers at low static magnetic fields

Giant magnetic circular dichroism (MCD) that shows a different response to incident wave with left or right-handed circular polarization under external magnetic field is promising for magneto-optical sensing, revealing symmetry and degeneracy information of electronic states. However, traditional methods and materials that are used to obtain significant MCD involve highly strong external magnetic field. Based on the excitation of subradiant plasmonic mode and Fano resonance in graphene oligomers in the mid-infrared region, we numerically demonstrate that MCD is enhanced three times larger than the previously reported method, based on the resonance of electric dipole plasmonic mode. This giant MCD is attributed to the remarkably different excitation efficiency of subdradiant plasmonic mode due to the interparticle coupling under left or right-handed circular polarization incidence and external magnetic field. Our results offer an effective mechanism to enhance MCD signal at the nanoscale, which facilitates the sensing, spintronic, nanophotonics and other such fields.