Multiband Nonreciprocal Radiation With Subwavelength Epsilon-Near-Zero Film

Nonreciprocal thermal radiation (NTR) holds great promise in revolutionizing energy harvesting and conversion process, which has become a hot topic of various research fields ranging from renewable energy, molecular sensing, to thermal circuitry and camouflage. The enhanced multiband nonreciprocal radiation in grating structure cooperated with epsilon-near-zero (ENZ) thin film and Weyl semimetal (WSM) layer backed by a metallic mirror has been proposed. It shows that traditional Kirchhoff's law of thermal radiation can be strongly broken with a larger contrast between emissivity and absorptivity at resonance wavelengths. The proposed structure can retain its functionality stably as a NTR device, and the dependence of the nonreciprocity spectra on the geometrical dimensions could be characterized as an effective method to tune NTR. The approach presented in this work could bring new means of engineering absorption, emission, and nonreciprocity in the mid-infrared (MIR) region.