Nonreciprocal Thermal Radiation from Magnetic Weyl Semimetals

Objects around us constantly emit and absorb thermal radiation. For reciprocal systems, the emissivity and absorptivity are restricted to be equal by Kirchhoff's law of thermal radiation. This restriction limits the control of thermal radiation and contributes to an intrinsic loss mechanism in photonic energy harvesting systems. Existing approaches to violate Kirchhoff's law typically utilize conventional magneto-optical effects in the presence of an external magnetic field. However, these approaches require either a strong magnetic field (~3T) [1] or narrow-band resonances under a moderate magnetic field (~0.3T) [2], because the non-reciprocity in conventional magneto-optical effects is usually 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 [3]. Such a thermal emitter can near completely violate Kirchhoff's law over broad angular and frequency ranges without requiring any external magnetic field.


[1] L. Zhu and S. Fan, Phys. Rev. B 90, 220301 (2014).
[2] B. Zhao, Y. Shi, J. Wang, Z. Zhao, N. Zhao, and S. Fan, Opt. Lett. 44, 17(2019).
[3] B. Zhao*, C. Guo*, C. A. C. Garcia, P. Narang, and S. Fan, Nano Lett. 20, 1923 (2020).