Magneto-optic perturbation theory for near-complete violation of Kirchhoff's law of thermal emission at low magnetic fields

TL;DR

This paper develops a perturbation theory to predict magneto-optical resonance shifts in plasmonic semiconductors, enabling the design of metasurfaces with near-complete violation of Kirchhoff's law at low magnetic fields.

Contribution

It introduces an analytical expression linking optical spin density and resonance shifts, facilitating the design of nonreciprocal thermal emitters with low magnetic field requirements.

Findings

Achieved a nonreciprocal emissivity contrast of 0.8 at 0.1 T

Derived an analytical formula for resonance shifts in magneto-optical systems

Explained differences in magnetic sensitivity among photonic structures

Abstract

Magneto-optic photonic systems can violate Kirchhoff's law of thermal emission by breaking Lorentz reciprocity. We develop a dispersive perturbation theory yielding an analytical expression for magneto-optical resonance frequency shifts in plasmonic semiconductors under applied magnetic fields. This expression shows the shift is governed by the overlap of the mode's optical spin density with the magneto-optical material. We use this expression to design a III-V metasurface that achieves nonreciprocal emissivity contrast of 0.8 at only 0.1 T, and demonstrate that the theory can explain order-of magnitude differences in magnetic field sensitivity between different photonic structures.