Mid-infrared strong nonreciprocal thermal radiation with extremely small applied magnetic field.

The ability to break the reciprocity between absorbance and emittance provides new ideas to develop advanced light harvesting devices and thermal management. However, the existing designs with magnetic optical (MO) materials typically require a magnetic excitation on the order of 1 T, which imposes a constraint on their practical application. Here, a photonic structure with a dielectric-MO material planar sandwiched between a dielectric resonator array and a metallic reflector is designed and studied. The results show that near-perfect nonreciprocity can be obtained with an extremely small magnetic excitation on the order of 0.2 T, which could be reached with permanent magnets. Moreover, the physical origin of such a phenomenon and the dependence of the thermal emission performances on the structural dimensions are also studied. The concepts and the results obtained here will pave the way for the development of nonreciprocal radiation devices with modest magnetic fields, which can be achieved in practice.