Title: Breakdown of the Kirchhoff's law of thermal radiation by a spatiotemporally modulated nonreciprocal metasurface Show Chinese title

Title: 由时空调制的非互易超表面对基尔霍夫热辐射定律的分解

Abstract: Kirchhoff's law of thermal radiation, which dictates that the emissivity of a surface equals its absorptivity under thermal equilibrium, which dictates that the emissivity of a surface equals its absorptivity under thermal equilibrium, fundamentally limits the efficiency of photonic systems by enforcing reciprocal energy exchange between source and detector. Breaking this reciprocity is particularly important for advancing photonic devices for energy conversion, radiative cooling, and mid-infrared sensing and imaging. Driven by the growing need for photonic platforms to overcome reciprocity constraints, we present the first demonstration of spatiotemporally modulated nonreciprocal metasurfaces operating at mid-infrared frequencies suitable for the violation of the Kirchhoff's law at room temperature. We fabricate a graphene-based integrated photonic structure and experimentally demonstrate nonreciprocal reflection from a metasurface modulated at gigahertz frequencies. We develop a theoretical framework to relate nonreciprocal scattering under spatiotemporal modulation with unequal absorptivity and emissivity for violation of the spectral directional Kirchhoff's law. Our experiment and theory imply effective decoupling of absorption and emission channels by breaking time-reversal symmetry at thermal wavelengths. Show Chinese abstract

Abstract: 基尔霍夫热辐射定律规定，在热平衡下，表面的发射率等于其吸收率，这从根本上限制了光子系统的效率，因为它强制源和探测器之间的互易能量交换。打破这种互易性对于推进用于能量转换、辐射冷却以及中红外传感和成像的光子器件尤为重要。由于对光子平台克服互易性约束的需求不断增长，我们展示了第一个在适合于室温下违反基尔霍夫定律的中红外频率下工作的时空调制非互易超表面的演示。我们制造了一个基于石墨烯的集成光子结构，并实验上展示了在千兆赫频率调制下的超表面的非互易反射。我们开发了一个理论框架，将时空调制下的非互易散射与不等的吸收率和发射率相关联，以违反光谱方向基尔霍夫定律。我们的实验和理论表明，通过在热波长处打破时间反演对称性，可以有效解耦吸收和发射通道。