Near-unity nonreciprocal thermal radiation in biaxial van der Waals material-Weyl semimetal heterostructures

Polaritons in natural van der Waals (vdW) materials have drawn significant attention as the unique optical properties and have opened doors for various potential applications. α-phase molybdenum trioxide (α-MoO3) has been revealed as a semiconducting anisotropic vdW material that holds great promise for manipulating orthogonal in-plane phonon polariton (PhP) modes in infrared (IR). Here, we consider an attenuated total reflection (ATR) geometry consisting of an α-MoO3 layer and a Weyl semimetal (WSM) interlayer sitting on a silver (Ag) substrate. The incorperated coupling prism is selected as KRS5 (thallium bromide-iodide) that can provide a larger wavevector. The spectral responses of the proposal have been investigated using electromagnetic (EM) simulations that utilize the anisotropic rigorous coupled-wave analysis (aRCWA). Our results demonstrate that the α-MoO3 thin layer can boost the constrast between the emissivity and absorptivity in a broad range of wavelength as compared to an uncoated device. The nonreciprocity at resonance wavelength can reach near-unity for both transverse electric (TE) and transverse magnetic (TM) wave incidence. The proposed α-MoO3/WSM heterostructure suggests great potentials for thermal radiation management with different demands.