Broad-angle nonreciprocal thermal radiation with reversible sign selection in planar Weyl semimetal structure

We propose a broad-angle nonreciprocal thermal emitter composed of ZnSe/Weyl semimetal (WSM)/AlN/Ge/ZnSe stacked on a metallic substrate. By harnessing the intrinsic time-reversal symmetry breaking in the WSM layer, the system exhibits strong nonreciprocal thermal emission in the mid-infrared range (6–9 μm), achieving an absolute average nonreciprocity exceeding 0.8 over a wide range of incident angles (10°–80°). Remarkably, the azimuthal angle ϕ serves as an effective tuning parameter for both the magnitude and sign of nonreciprocity. At ϕ=0°, nonreciprocity is observed exclusively under transverse magnetic (TM) polarization. As ϕ increases, the response undergoes a sign reversal in which transverse electric polarization exhibits positive nonreciprocity, whereas TM switches to negative nonreciprocity. This polarization-dependent sign tunability offers a promising avenue for dynamically controlling nonreciprocal thermal radiation.