Observation of optical gyromagnetic properties in a magneto-plasmonic metamaterial

TL;DR

This paper reports the first observation of gyromagnetic properties in a magneto-plasmonic metamaterial at near-infrared wavelengths, enabling control over optical magnetic responses and potential applications in nonreciprocal photonics.

Contribution

The study demonstrates the experimental realization of a gyromagnetic permeability tensor with non-zero off-diagonal elements in a metamaterial at optical frequencies, which was previously unobserved.

Findings

Effective off-diagonal permeability tensor elements reach 10^-3 at resonance.

Transverse magneto-optical Kerr effect (TMOKE) observed under s-polarized incidence.

Gyromagnetic properties are attributed to local electric field modulation by split-ring resonators.

Abstract

Metamaterials with artificial optical properties have attracted significant research interest. In particular, artificial magnetic resonances in non-unity permeability tensor at optical frequencies in metamaterials have been reported. However, only non-unity diagonal elements of the permeability tensor have been demonstrated to date. A gyromagnetic permeability tensor with non-zero off-diagonal elements has not been observed at the optical frequencies. Here we report the observation of gyromagnetic properties in the near-infrared wavelength range in a magneto-plasmonic metamaterial. The non-zero off-diagonal permeability tensor element causes the transverse magneto-optical Kerr effect (TMOKE) under s-polarized incidence that otherwise vanishes if the permeability tensor is not gyromagnetic. By retrieving the permeability tensor elements from reflection, transmission, and TMOKE spectra, we show that the effective off-diagonal permeability tensor elements reach the 10-3 level at the resonance wavelength (~900 nm) of the split-ring resonators that is at least two orders of magnitude higher than that of magneto-optical materials at the same wavelength. The artificial gyromagnetic permeability is attributed to the change in the local electric field direction modulated by the split-ring resonators. Our study demonstrates the possibility of engineering the permeability and permittivity tensors in metamaterials at arbitrary frequencies, thereby promising a variety of applications of next-generation nonreciprocal photonic devices, magneto-plasmonic sensors, and active metamaterials.