Multi-channel wide-angle nonreciprocal thermal radiator with planar heterostructure

Abstract

From the perspective of application at mid-infrared frequencies, omnidirectional nonreciprocal thermal radiation represents a critical need for effective thermal energy harvesting. In this study, we propose a nonreciprocal thermal radiator (NTR) which can be fabricated with a lithography-free approach. The structure is composed by germanium(Ge)-aluminum nitride(AlN)-Weyl semimetal (WSM) stacks and terminated with a metallic substrate. The results indicate that both the magnitude and the sign of the contrast between emission ($e$) and absorption ($\alpha$) can be manipulated. This design achieves multi-channel nonreciprocal stability for transverse magnetic (TM) polarized incident wave over an exceptionally wide angular range. Additionally, the electromagnetic field distributions at the resonance wavelengths have been analyzed to elucidate the underlying principles. Multi-band nonreciprocity under transverse electric (TE) polarized incident wave has also been obtained. The capability of our proposal offers a relatively straightforward method to realize high-performance NTR. This advancement holds potential implications for the development of efficient energy harvesting and conversion devices.