Xu Liujun, Zhuang Pengfei, Yang Fubao, Yang Shuihua, Wang Chengmeng, Dai Gaole, Huang Jiping, Qiu Cheng-Wei
Graduate School of China Academy of Engineering Physics, Beijing 100193, China.
Fudan University, Department of Physics, State Key Laboratory of Surface Physics, and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Shanghai 200438, China.
Phys Rev Lett. 2025 Aug 8;135(6):067103. doi: 10.1103/cny8-szn7.
Topological invariants have been utilized profoundly to classify the geometric features of electronic, photonic, and phononic structures. However, no invariant has ever been conceptualized to classify the functional properties of diverse thermal structures. Here, we formulate a heat diffusion invariant to reveal the explicit correlation between thermal functionality and diffusivity. The value goes beyond establishing a unified framework for various thermal metamaterials. The heat diffusion invariant offers a forward paradigm for precisely achieving freeform transient thermal metamaterials with isotropic thermal conductivity. We verify the competitiveness and robustness experimentally via a freeform transient thermal cloak. The heat diffusion invariant also paves the way for other functions, such as transient thermal illusion, and applies to thermal convection and radiation. These findings could open up an unprecedented invariant-based gateway to thermal management, metamaterial design, and nonequilibrium energy and mass transport.
拓扑不变量已被广泛用于对电子、光子和声子结构的几何特征进行分类。然而，尚未有任何不变量被概念化用于对各种热结构的功能特性进行分类。在此，我们制定了一个热扩散不变量，以揭示热功能与扩散率之间的明确关联。该值不仅为各种热超材料建立了一个统一框架。热扩散不变量为精确实现具有各向同性热导率的自由形式瞬态热超材料提供了一个前沿范例。我们通过一个自由形式瞬态热斗篷在实验上验证了其竞争力和稳健性。热扩散不变量还为其他功能，如瞬态热错觉，铺平了道路，并适用于热对流和热辐射。这些发现可能为热管理、超材料设计以及非平衡能量和质量输运打开一个前所未有的基于不变量的大门。
