Strong Nonreciprocal Thermal Radiation Within Atmospheric Window With Lithography-Free Structure

Realizing a mid-infrared (mid-IR) nonreciprocal thermal emitter (NTE) within atmospheric window is a promising yet challenging task. Here we theoretically explore the enhanced contrast between emission and absorption of a resonant system with Weyl semimetal (WSM). We propose and present a lithography-free approach for manipulating the nonreciprocal thermal radiation (NTR), which also leads to near-zero emission and near-unity absorption simultaneously. It shows that the reciprocity between absorption and emission can be strongly broken with the difference of 0.973 at wavelength of $13.6~\mu m$ . By examining the impact of geometrical parameters, the structure manifests large parameter tolerance, which is advantageous for practical fabrication and application. The influence of incidence angle and azimuthal angle on the nonreciprocity has been also been investigated. The presented results offer new insights into engineering absorption and emission, that can facilitate the design of NTE in the mid-IR region.