Near-infrared nonreciprocal thermal emitters induced by asymmetric embedded eigenstates

Engineering nonreciprocal thermal radiation is of great importance in both fundamental thermal science and practical energy applications, but the design of perfect nonreciprocal thermal emitters in the near-infrared region has not been reported due to considerably weak magneto-optical (MO) responses of natural materials. In this work, by taking advantage of high-Q asymmetric embedded eigenstates (EEs) and quasi-EEs, near-complete violation of Kirchhoff’s law has been achieved within the near-infrared waveband using epsilon-near-zero/MO dielectric/metal sandwich structures. The analytical dispersion relations of guided modes are firstly derived, perfectly predicting the asymmetric resonant peaks in absorption or emission spectra. We also establish explicit rules to build the connections between angular locations of EEs and the thickness of MO dielectric layer, which allows to flexibly tailor perfect nonreciprocal properties over a wide angular range. Besides, the influence of upper layer’s thickness, material loss and different substrates in asymmetric distributions of EEs has also been discussed. The unveiled mechanisms and tunability in engineering nonreciprocal thermal radiation might pave a new way for the next-generation energy devices to break the current limit of energy transfer and conversion efficiency.