Exceptionally high Verdet constant in gold nanodisc arrays

Magneto-optical effects in non-magnetic noble metals can be invoked by leveraging the in-plane Lorentz force at engineered plasmonic resonances. We demonstrate a 2-D array of gold nanodiscs designed to host a hybrid resonance of localized plasmon and surface lattice modes. The structure exhibits a Verdet constant of 1.98 × 10⁶°·T^-1 m^-1, corresponding to a Faraday rotation of -0.15° at a 1 T magnetic field. This Verdet constant represents a 15-fold enhancement over a continuous, unpatterned gold film of the same thickness measured under identical conditions and is highly competitive with many plasmon-enhanced diamagnetic nanostructures. Numerical simulations show that the magnetic field independent rotation is due to structure imperfections and thus with better tolerance in nanofabrication, one could get much higher absolute Faraday rotation at these resonances. These findings offer new opportunities for harnessing strong magneto-plasmonic effects in optoelectronic devices by patterning non-magnetic metal contacts.