Ultra-small-angle nonreciprocal thermal radiation via bound states in the continuum-driven topological phase singularity pairs without magneto-optical dielectrics

With recent advances in solar technology, small-angle nonreciprocal thermal radiation (NTR) devices have attracted extensive research interest. However, conventional NTR devices typically rely on specialized magneto-optical (MO) materials, which limits their applicability. In this Letter, a tilted multilayer metastructure-photonic crystal (TMMPC) based on common dielectric and metallic silver configurations is proposed. Without employing any MO dielectrics, the TMMPC supports NTR under two polarization modes and achieves a nonreciprocity of 0.98 at an ultra-small incident angle of 0.3°. Furthermore, the controlled motion, annihilation, and revival of topological phase singularity pairs driven by bound states in the continuum are demonstrated in the TMMPC. Such phenomena confirm that TMMPC achieves the NTR effect, analogous to the behavior of conventional MO materials, without incorporating any MO dielectric constituents. These suggest the potential of the TMMPC as a MO metastructure-photonic crystal platform for applications in nonreciprocal devices, photovoltaics, and optical communication.