Broadband and wide angle nonreciprocal thermal emission from Weyl semimetal structures

Abstract

Nonreciprocal thermal emission is a cutting-edge technology that enables fundamental control over thermal radiation and has exciting applications in thermal energy harvesting. However, thus far one of the foremost challenges is making nonreciprocal emission operate over a broad wavelength range and for multiple angles. In this work, we solve this outstanding problem by proposing three different types of structures that always utilize only one Weyl semimetal (WSM) thin film combined with one or two additional dielectric or metallic layers and terminated by a metallic substrate. First, a tradeoff relationship between the magnitude and bandwidth of the thermal nonreciprocity contrast is established based on the thickness of the WSM film. Then, the bandwidth broadening effect is demonstrated via the insertion of a dielectric spacer layer that can also be fine-tuned by varying its thickness. Finally, further control on the resulting strong nonreciprocal thermal radiation is demonstrated by the addition of a thin metallic layer in the proposed few layer designs. The presented composite structures work for a broad frequency range and for multiple emission angles, resulting in highly advantageous properties for various nonreciprocal thermal radiation applications. Moreover, the proposed designs do not require any patterning and can be experimentally realized by simple deposition fabrication methods. They are expected to aid in the creation of broadband nonreciprocal thermal emitters that can find applications in new energy harvesting devices.

Wide-angle and Fano-shape contrast between emission and absorption in hybrid polariton-involved planar structure

“…Thus, the nonreciprocal property disappears under these two configurations that represent the limits of nonreciprocity. Until now, most of the research on NLP concerned with ppolarized incidence wave [36,63,64]. Considering the promising applications of NLP, it is necessary to generate strong nonreciprocity for both s-and p-polarized incidence waves [65].…”

“…To alleviate the requirement of strong magnetic fields, magnet-free NRMs are extremely appreciated for new strategy to accomplish the strong nonreciprocity without any external stimulus [32,33]. Quite recently, Weyl semimetals (WSMs) have drawn much attention to improve the nonreciprocal properties [34][35][36][37][38]. It is also should be pointed out that complex nano-patterning or multilayer deposition methods need to be employed to achieve previously mentioned goals that are very difficult to implement in practice [39][40][41][42][43], especially the WSM is still immature in term of fabrication.…”