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The reciprocity between thermal emission and absorption in materials that satisfy the Lorentz reciprocity places a fundamental constraint on photonic energy conversion and thermal management. For approaching the ultimate thermodynamic limits in various photonic energy conversions and achieving nonreciprocal radiative thermal management, broadband nonreciprocal thermal emission is desired. However, existing designs of nonreciprocal emitters are narrowband. Here, we introduce a gradient epsilon-near-zero magneto-optical metamaterial for achieving broadband nonreciprocal thermal emission. We start by analyzing the nonreciprocal thermal emission and absorption in a thin layer of epsilon-near-zero magneto-optical material atop a substrate. We use temporal coupled-mode theory to elucidate the mechanism of nonreciprocal emission in the thin-film emitter. We then introduce a general approach for achieving broadband nonreciprocal emission by using a gradient epsilon-near-zero magnetooptical metamaterial. We numerically demonstrate broadband nonreciprocal emission in gradient-doped semiconductor multilayer, as well as in a magnetic Weyl semimetal multilayer with gradient chemical potential. Our approach for achieving broadband nonreciprocal emitters is useful for developing broadband nonreciprocal devices for energy conversion and thermal management.
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Broadband and wide angle nonreciprocal thermal emission from Weyl semimetal structures
Nonreciprocal thermal emission is a cutting-edge technology that enables fundamental control over thermal radiation and has exciting applications in thermal energy harvesting. However, thus far one of the foremost challenges is making nonreciprocal emission operate over a broad wavelength range and for multiple angles. In this work, we solve this outstanding problem by proposing three different types of structures that always utilize only one Weyl semimetal (WSM) thin film combined with one or two additional dielectric or metallic layers and terminated by a metallic substrate. First, a tradeoff relationship between the magnitude and bandwidth of the thermal nonreciprocity contrast is established based on the thickness of the WSM film. Then, the bandwidth broadening effect is demonstrated via the insertion of a dielectric spacer layer that can also be fine-tuned by varying its thickness. Finally, further control on the resulting strong nonreciprocal thermal radiation is demonstrated by the addition of a thin metallic layer in the proposed few layer designs. The presented composite structures work for a broad frequency range and for multiple emission angles, resulting in highly advantageous properties for various nonreciprocal thermal radiation applications. Moreover, the proposed designs do not require any patterning and can be experimentally realized by simple deposition fabrication methods. They are expected to aid in the creation of broadband nonreciprocal thermal emitters that can find applications in new energy harvesting devices.
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- Award ID(s):
- 2224456
- PAR ID:
- 10496823
- Publisher / Repository:
- Optica Publishing Group
- Date Published:
- Journal Name:
- Journal of the Optical Society of America B
- Volume:
- 40
- Issue:
- 8
- ISSN:
- 0740-3224
- Page Range / eLocation ID:
- 2122
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1364/JOSAB.495725
