A chiral absorber of light can emit spin-polarized (circularly polarized) thermal radiation based on Kirchhoff's law which equates spin-resolved emissivity with spin-resolved absorptivity for reciprocal media at thermal equilibrium. No such law is known for nonreciprocal media. In this work, we discover three spin-resolved Kirchhoff's laws of thermal radiation applicable for both reciprocal and nonreciprocal planar media. In particular, these laws are applicable to multi-layered or composite slabs of generic bianisotropic material classes which include (uniaxial or biaxial) birefringent crystals, (gyrotropic) Weyl semimetals, magnetized semiconductors, plasmas, ferromagnets and ferrites, (magnetoelectric) topological insulators, metamaterials and multiferroic media. We also propose an experiment to verify these laws using a single system of doped Indium Antimonide (InSb) thin film in an external magnetic field. Furthermore, we reveal a surprising result that the planar slabs of all these material classes can emit partially circularly polarized thermal light without requiring any surface patterning, and identify planar configurations which can experience nontrivial thermal optomechanical forces and torques upon thermal emission into the external environment at lower temperature (nonequilibrium). Our work also provides a new fundamental insight of detailed balance of angular momentum (in addition to energy) of equilibrium thermal radiation, and paves the way for practical functionalities based on thermal radiation using nonreciprocal bianisotropic materials.

中文翻译：

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非互易双各向异性介质的通用自旋分辨热辐射定律

根据基尔霍夫定律，光的手性吸收剂可以发射自旋偏振（圆偏振）热辐射，基尔霍夫定律将自旋分辨发射率与热平衡下互易介质的自旋分辨吸收率相等。对于非互惠媒体，没有这样的法律。在这项工作中，我们发现了适用于互易和非互易平面介质的三个自旋分辨基尔霍夫热辐射定律。特别是，这些定律适用于通用双各向异性材料类别的多层或复合板，包括（单轴或双轴）双折射晶体、（回旋）外尔半金属、磁化半导体、等离子体、铁磁体和铁氧体、（磁电）拓扑绝缘体、超材料和多铁性介质。我们还提出了一个实验来验证这些定律，在外部磁场中使用单一系统的掺杂锑化铟 (InSb) 薄膜。此外，我们揭示了一个令人惊讶的结果，即所有这些材料类别的平面板都可以发射部分圆偏振热光，而无需任何表面图案，并确定平面配置，这些配置可以在热辐射到外部环境时经历非平凡的热光机械力和扭矩较低的温度（非平衡）。我们的工作还为平衡热辐射的角动量（除了能量）的详细平衡提供了新的基本见解，并为基于使用非互易双各向异性材料的热辐射的实用功能铺平了道路。