Large nonreciprocity of thermal radiation for transverse electric wave with extremely small incident angle

Violating of traditional Kirchhoff's law has been a topic of active research because of the possibilities for engineering thermal radiation. An alternative paradigm consisting of zero-contrast gratings (ZCGs) and Weyl semimetal (WSM) interlayer sitting on a silver (Ag) substrate is proposed. Strong nonreciprocal thermal radiation (NTR) has been observed for transverse electric (TE) incidence wave. This structure is highly favorable for standard mask-based nano-fabrication processes. Moreover, the nonreciprocity larger than 0.8 is realized with an extremely small angle of 1 degrees. The mechanism of this proposal is owing to the guided mode resonance (GMR) supported by the ZCGs and nonreciprocal radiation of WSM, which is confirmed by investigating the amplitude distribution of electric field. The high performance of the NTR can be maintained within wide ranges of structural parameters, which is highly favorable for practical fabrication. The nonreciprocal emitter described herein allows simultaneous control of spectral distribution and polarization of radiation, which will facilitate the active design and application of mid-infrared (MIR) thermal emitters.