Recent experiments have realized exciton condensation in bilayer materials such as graphene double layers and the van der Waals heterostructure MoSe₂–WSe₂ with the potential for nearly frictionless energy transport. Here we computationally observe the microscopic beginnings of exciton condensation in a molecular-scale fragment of MoSe₂–WSe₂, using advanced electronic structure methods based on reduced density matrices. We establish a connection between the signature of exciton condensation—the presence of a large eigenvalue in the particle-hole reduced density matrix—and experimental evidence of exciton condensation in the material. The presence of a “critical seed” of exciton condensation in a molecular-scale fragment of a heterostructure bilayer provides insight into how local short-range strongly correlated effects may give rise to macroscopic exciton condensation. We find that molecular-scale properties such as layer alignment and interlayer distance can impact the formation of nonclassical long-range order in heterostructure bilayers, demonstrating the importance of geometric considerations for the rational design of exciton condensate materials. Mechanistic insights into the microscopic origins of exciton condensation have potential implications for the design and development of new materials with enhanced energy transport properties.

中文翻译：

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范德华异质结构双层中激子缩合的分子起源


最近的实验在双层材料（如石墨烯双层和范德华异质结构 MoSe 2-WSe ₂）中实现了激子凝聚，具有几乎无摩擦能量传输的潜力。在这里，我们使用基于减密度矩阵的先进电子结构方法，通过计算观察 MoSe 2-WSe ₂ 分子尺度片段中激子缩合的微观开始。我们在激子凝聚的特征（颗粒空穴减密度矩阵中存在大特征值）与材料中激子凝聚的实验证据之间建立了联系。异质结构双层的分子尺度片段中存在激子凝聚的“关键种子”，这为局部短程强相关效应如何引起宏观激子凝聚提供了见解。我们发现分子尺度特性（如层排列和层间距离）会影响异质结构双层中非经典长程顺序的形成，证明了几何考虑对于激子凝聚态材料的合理设计的重要性。对激子凝聚的微观起源的机理见解对具有增强能量传输特性的新材料的设计和开发具有潜在意义。