Excitons with nonzero momenta and their energy dependence are important for time dependent phenomena such as transport properties or the coupling to external or internal fields, for example in electron energy loss spectroscopy. In this paper we calculate the momentum dependent energy landscape of excitons in rubrene single crystals. We show that singlet excitons exhibit a dispersion that is qualitatively similar to the electronic valence and conduction bands, namely a relatively large bandwidth along $\mathrm{\Gamma }$–Y and much flatter bands along $\mathrm{\Gamma }$–X and $\mathrm{\Gamma }$–Z. However, the absolute value of the bandwidths is significantly weaker than for both electronic bands. Triplet excitons, on the other hand, show much less dispersion and the exciton bands are much flatter than their singlet counterparts.

中文翻译：

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红荧烯单晶中的有限动量激子

具有非零动量的激子及其能量依赖性对于时间相关现象很重要，例如传输特性或与外部或内部场的耦合，例如在电子能量损失光谱中。在本文中，我们计算了红荧烯单晶中激子的动量相关能量图谱。我们表明单线态激子表现出与电子价带和导带定性相似的色散，即沿$\mathrm{\Gamma }$–Y 和更平坦的带 $\mathrm{\Gamma }$–X 和 $\mathrm{\Gamma }$-Z。然而，带宽的绝对值明显弱于两个电子带。另一方面，三重态激子的色散要小得多，激子带比它们的单重态对应物要平坦得多。