单线态裂变中的集体激子纠缠
Collective Excitonic Entanglement in Singlet Fission
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中文总结 AI 辅助
本研究建立统一框架，揭示单线态裂变源于集体激子纠缠，利用粒子-空穴约化密度矩阵分析材料关联，阐明结构对机制的调控，为理解单线态裂变起源提供新视角。
中文摘要 AI 辅助
单线态裂变是指一个单线态激子转化为两个三线态激子的过程，它有望通过将太阳能电池效率提升至 Shockley-Queisser 极限以上，彻底变革太阳能生产。然而，单线态裂变的实际应用仍是一项重大挑战，其内在机制长期存在争议。本文表明，单线态裂变源于一种独特的集体激子纠缠：激子凝聚为单一粒子-空穴模式，其原理与激子的玻色-爱因斯坦凝聚相同。从定量角度看，这种凝聚表现为粒子-空穴约化密度矩阵（RDM）的一个大特征值，代表多个激子占据同一集体模式。我们利用粒子-空穴 RDM 捕捉并五苯晶体、共价连接的并五苯二聚体等单线态裂变材料中固有的粒子-空穴关联，揭示结构变化如何调控单线态裂变机制并调节电荷转移态的贡献。单一模式中激子布居的这种特征增强，在激子凝聚的起始阶段和光合能量转移机制中均普遍存在。综上，我们的研究建立了一个统一框架，用于从集体激子纠缠的角度理解单线态裂变的起源。
英文摘要
Singlet fission, the conversion of one singlet exciton into two triplet excitons, has the potential to revolutionize solar energy production by boosting the efficiency of solar cells beyond the Shockley-Queisser limit. However, the practical realization of singlet fission remains an outstanding challenge, and its underlying mechanisms have long been debated. Here we show that singlet fission arises from a distinctive type of collective excitonic entanglement in which the excitons condense into a single particle-hole mode, the same principle that leads to the Bose-Einstein condensation of excitons. Quantitatively, this condensation appears as a large eigenvalue of the particle-hole reduced density matrix (RDM), representing multiple excitons occupying a collective mode. We utilize the particle-hole RDM to capture the intrinsic particle-hole correlations in singlet fission materials including acene crystals and covalently linked pentacene dimers, revealing how structural changes control singlet fission mechanisms and modulate the contributions of charge transfer states. The same characteristic enhancement of excitonic population in a single mode is common to the onset of exciton condensation and the mechanism of photosynthetic energy transfer. Together, our results establish a unifying framework for understanding the origins of singlet fission in terms of collective excitonic entanglement.
