Prominent nonreciprocity in metasurfaces supported by dielectric-coated Weyl semimetal substrates

Magnetless nonreciprocal radiation in the structures consisting of Weyl semimetal attracted much attention in modern photonics, and the major issue in this research direction is to achieve strong nonreciprocity for a wide range of angles. In this Letter, we theoretically show that dielectric metasurfaces supported by dielectric-coated Weyl semimetal substrates exhibit prominent nonreciprocity. The spectral separation between the emissivity and absorptivity peaks is more than 6 times their spectral widths. In particular, the peak value of the difference between the emissivity and absorptivity amounts to more than 0.5 even for a small angle of 8° and it sustains near-unity over nearly all angles. The contribution of a resonantly excited surface plasmon polariton and the significant role of a dielectric film on the Weyl semimetal substrate have been thoroughly analyzed. We believe that the results are an important step toward practical applications of magnet-free nonreciprocal thermal photonics, including heat transfer, sensing, and radiative cooling.