Near-perfect nonreciprocal radiation with a 0.3 T magnetic field for near normal incidence

Abstract

Breaking the traditional Kirchhoff’s law opens new avenues for enhancing energy harvesting efficiency and advancing thermal management. However, current approaches that violating Kirchhoff’s law by using magnetic optical materials (MO) often face challenges due to the necessity of strong magnetic excitation and large incident angles, which limit their practical applications. We propose a novel photonic design featuring a cascaded metal-dielectric periodic resonant array situated on a dielectric-MO material planar structure backed with a metallic reflector. This design achieves significant nonreciprocity between absorptivity and emissivity for near-normal incident light with only a 0.3 T magnetic field strength. The required magnetic excitation can be conveniently provided by a permanent magnet, thereby facilitating real-world implementations. Furthermore, this effect can be attributed to guided mode resonance, as confirmed by the distributions of the magnetic field magnitude. Additionally, we investigate how geometrical dimensions influence nonreciprocal radiation properties. These findings offer new opportunities for the development of nonreciprocal radiation devices capable of operating under near-normal incidence with moderate magnetic excitation, making them suitable for practical implementation.