Kirchhoff Thermal Radiation Law Violation via Resonant Absorption in Hybrid Magneto-Optic InAs Guided-Mode-Resonator Structure

The Kirchhoff thermal radiation law provides an inherent constraint on the ability to harness thermal radiation, requiring that the spectral emissivity and absorptivity are equal and exhibit identical angular distributions for a given polarization. This equality is built on the fundamental assumption that all materials obey Lorentz reciprocity. One class of materials that does not satisfy Lorentz reciprocity, and thus can violate the Kirchhoff law, is magneto-optically-active materials. In this work, we break time-reversal symmetry and reciprocity in degenerately n-type doped magneto-optic InAs with a static magnetic field where light coupling is mediated by a guided-mode-resonator structure whose resonant frequency coincides with the epsilon-near-zero resonance of the doped InAs. Using an Otto scattering configuration, we observe the nonreciprocal absorptive/emissive behavior as a function of magnetic field and scattering angle in the long-wavelength infrared region. Accounting for resonant and nonresonant optical scattering, we reliably model experimental results that violate the Kirchhoff thermal radiation law and discuss direct thermal emission of magneto-optic materials.