The ability to break Kirchhoff’s law is of fundamental importance in thermal radiation. Various nonreciprocal emitters have been proposed to break the balance between absorption and emission. However, the thicknesses of the nonreciprocal materials are usually larger than 1/10 times of the wavelength. Besides, the previous proposed nonreciprocal emitters are complex, thus they can hardly be fabricated in experiment to verify the Kirchhoff’s law for nonreciprocal materials. In this paper, we investigate the nonreciprocal thermal radiation of the magnetic Weyl semimetal (MWSM) film atop of the metal substrate. It is found that the strong nonreciprocal radiation at the wavelength of 9.15 µm can be achieved when the thickness of the MWSM film is 100 nm. The enhanced nonreciprocity is attributed to the Fabry-Perot resonances. The results indicate that the MWSM film is the promising candidate to engineer the ultrathin and simple nonreciprocal thermal emitters. What is perhaps most intriguing here is that the proposed structure can be more easily fabricated in experiment to verify the Kirchhoff’s law for nonreciprocal materials.

中文翻译：

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在超薄磁性外尔半金属薄膜中几乎完全违反基尔霍夫热辐射定律

打破基尔霍夫定律的能力在热辐射中至关重要。已经提出了各种非互易发射器来打破吸收和发射之间的平衡。然而，非互易材料的厚度通常大于波长的 1/10 倍。此外，先前提出的非互易发射器很复杂，因此很难在实验中制造它们来验证非互易材料的基尔霍夫定律。在本文中，我们研究了金属基材顶部磁性外尔半金属 (MWSM) 膜的非互易热辐射。发现当 MWSM 薄膜厚度为 100 nm 时，可以实现 9.15 µm 波长处的强非互易辐射。增强的非互易性归因于法布里-珀罗共振。结果表明，MWSM 薄膜是设计超薄和简单的非互易热发射器的有希望的候选者。这里最有趣的可能是所提出的结构可以更容易地在实验中制造，以验证非互易材料的基尔霍夫定律。