Title: Large Cumulant Eigenvalue as a Signature of Exciton Condensation Show Chinese title

Title: 大累积量特征值作为激子凝聚的标志

Abstract: The Bose-Einstein condensation of excitons into a single quantum state is known as exciton condensation. Exciton condensation, which potentially supports the frictionless flow of energy, has recently been realized in graphene bilayers and van der Waals heterostructures. Here we show that exciton condensates can be predicted from a combination of reduced density matrix theory and cumulant theory. We show that exciton condensation occurs if and only if there exists a large eigenvalue in the cumulant part of the particle-hole reduced density matrix. In the thermodynamic limit we show that the large eigenvalue is bounded from above by the number of excitons. In contrast to the eigenvalues of the particle-hole matrix, the large eigenvalue of the cumulant matrix has the advantage of providing a size-extensive measure of the extent of condensation. Here we apply this signature to predict exciton condensation in both the Lipkin model and molecular stacks of benzene. The computational signature has applications to the prediction of exciton condensation in both molecules and materials. Show Chinese abstract

Abstract: 准粒子在单个量子态中的玻色-爱因斯坦凝聚被称为激子凝聚。 激子凝聚有可能支持无摩擦的能量流动，最近已在石墨烯双层和范德华异质结构中实现。 在这里，我们表明，激子凝聚可以从约化密度矩阵理论和累积理论的结合中预测出来。 我们表明，只有当粒子-空穴约化密度矩阵的累积部分存在一个大的本征值时，才会发生激子凝聚。 在热力学极限下，我们证明该大本征值被激子数量从上方限制。 与粒子-空穴矩阵的本征值相比，累积矩阵的大本征值具有提供凝聚程度的大小广延度量的优势。 在这里，我们将这一特征应用于预测利普金模型和苯分子堆栈中的激子凝聚。 计算特征可用于预测分子和材料中的激子凝聚。