Strong broadband nonreciprocal thermal radiation in multilayer gradient magneto-optical structure

Nonreciprocal thermal radiation, which violates symmetric reciprocity of traditional Kirchhoff's law, possesses numerous potential applications such as infrared camouflage and thermophotovoltaics. Here, we propose a multilayer structure composed of periodically stacked gradient doping concentration InAs layers and dielectric layers. Numerical simulations indicate that the proposed structure achieves strong broadband nonreciprocal thermal radiation at 18–20 μm, with average absorption, emission, and nonreciprocal performance of 0.29, 0.92, and 0.63, respectively. Such outstanding performance is attributed to the coupling of the epsilon-near-zero effect and Fabry–Pérot resonance, which can be demonstrated in the magnetic field distribution. The effects of incident angle, structural parameters, and magnetic field on nonreciprocal performance are also analyzed. We believe that this work paves the way for broadband, nonreciprocal thermal radiation, opening up new opportunities in fields such as energy utilization.