Zhao Bo, Guo Cheng, Garcia Christina A C, Narang Prineha, Fan Shanhui
Department of Electrical Engineering, Ginzton Laboratory, Stanford University, Stanford, California 94305, United States.
Department of Applied Physics, Stanford University, Stanford, California 94305, United States.
Nano Lett. 2020 Mar 11;20(3):1923-1927. doi: 10.1021/acs.nanolett.9b05179. Epub 2020 Feb 24.
Objects around us constantly emit and absorb thermal radiation. The emission and absorption processes are governed by two fundamental radiative properties: emissivity and absorptivity. For reciprocal systems, the emissivity and absorptivity are restricted to be equal by Kirchhoff's law of thermal radiation. This restriction limits the degree of freedom to control thermal radiation and contributes to an intrinsic loss mechanism in photonic energy harvesting systems. Existing approaches to violate Kirchhoff's law typically utilize magneto-optical effects with an external magnetic field. However, these approaches require either a strong magnetic field (∼3T) or narrow-band resonances under a moderate magnetic field (∼0.3T), because the nonreciprocity in conventional magneto-optical effects is weak in the thermal wavelength range. Here, we show that the axion electrodynamics in magnetic Weyl semimetals can be used to construct strongly nonreciprocal thermal emitters that nearly completely violate Kirchhoff's law over broad angular and frequency ranges without requiring any external magnetic field.
我们周围的物体不断地发射和吸收热辐射。发射和吸收过程由两个基本的辐射特性决定：发射率和吸收率。对于互易系统，根据基尔霍夫热辐射定律，发射率和吸收率被限制为相等。这种限制限制了控制热辐射的自由度，并导致了光子能量收集系统中的固有损耗机制。现有的违反基尔霍夫定律的方法通常利用外部磁场的磁光效应。然而，这些方法要么需要强磁场（约3T），要么在中等磁场（约0.3T）下需要窄带共振，因为传统磁光效应中的非互易性在热波长范围内较弱。在这里，我们表明，磁性外尔半金属中的轴子电动力学可用于构建强非互易热发射器，该发射器在宽角度和频率范围内几乎完全违反基尔霍夫定律，而无需任何外部磁场。
