Maximum non reciprocity in metasurfaces of gyrotropic rods

Efficiently breaking time-reversal symmetry at the subwavelength scale remains a cornerstone challenge for advanced electromagnetic wave manipulation.

This work presents a rigorous analytical framework, based on cylindrical wave expansion, to investigate and optimize the nonreciprocal scattering of transverse electric waves by magnetically biased plasmonic rods.

An intuitive metric is introduced to quantify the breaking of time-reversal symmetry via the asymmetric lifting of degeneracy between azimuthal modes of opposite angular momentum, hosted by the gyrotropic particles.

Leveraging this metric, a comprehensive mapping of the multiparametric space of operational frequency, cyclotron frequency, and cylinder optical size isolates regimes of maximum nonreciprocity.

A detailed multipolar decomposition reveals that this extreme behavior stems from the phase-matched asymmetric excitation and interference of localized electric and magnetic dipole modes.

Moving from individual, isolated meta-atoms to collective photonic systems, the optimized cylinders are arranged into a periodic grating.

Under oblique incidence, the combination of geometric asymmetry and magnetic mode splitting, forces the metasurface to transmit light in a totally different way when excited by opposite sides.

The reported findings and design principles offer a versatile blueprint for the development of dynamically tunable flat-optics isolators, directional transceivers, and advanced wavefront routers.