Their exceptional optical properties are a driving force for the persistent interest in atomically thin transition metal dichalcogenides such as MoS₂. The optical response is dominated by excitons. Apart from the bright excitons, which directly couple to light, it has been realized that dark excitons, where photon absorption or emission is inhibited by the spin state or momentum mismatch, are decisive for many optical properties. However, in particular the momentum dependence is difficult to assess experimentally and often remains elusive or is investigated by indirect means. Here we study the momentum dependent electronic structure experimentally and theoretically. We use angle-resolved photoemission as a one-particle probe of the occupied valence band structure and electron energy loss spectroscopy as a two-particle probe of electronic transitions across the gap to benchmark a single-particle model of the dielectric function \(\epsilon ({\bf{q}},\omega )\) against momentum dependent experimental measurements. This ansatz captures key aspects of the data surprisingly well. In particular, the energy region where substantial nesting occurs, which is at the origin of the strong light–matter interaction of thin transition metal dichalcogenides and crucial for the prominent C-exciton, is described well and spans a more complex exciton landscape than previously anticipated. Its local maxima in \(({\bf{q}}\ \ne \ 0,\omega )\) space can be considered as dark excitons and might be relevant for higher order optical processes. Our study may lead to a more complete understanding of the optical properties of atomically thin transition metal dichalcogenides.

它们出色的光学性能是人们对原子薄的过渡金属二卤化金属（例如MoS _2）的持续关注的驱动力。光学响应主要由激子决定。除了直接与光耦合的明亮的激子外，人们还认识到，黑暗的激子对许多光学性质起着决定性作用，其中自旋态或动量失配抑制了光子的吸收或发射。但是，尤其是动量依赖关系很难通过实验进行评估，并且常常难以捉摸，或者通过间接方式进行研究。在这里，我们通过实验和理论研究动量相关的电子结构。我们使用角分辨光发射作为占据价带结构的单粒子探针，并使用电子能量损失谱作为跨间隙电子跃迁的两粒子探针，以对介电函数\（\ epsilon （{\ bf {q}}，\ omega）\）反对动量依赖的实验测量。这种ansatz可以很好地捕获数据的关键方面。特别是，很好地描述了发生大量嵌套的能量区域，该能量区域是薄过渡金属二硫化碳的强光-物质相互作用的起点，并且对于突出的C激子至关重要，它涵盖了比以前预期的更复杂的激子态势。 。它在\（（{{bf {q}} \\ ne \ 0，\ omega} \）空间中的局部最大值可被视为暗激子，可能与高阶光学过程有关。我们的研究可能会导致对原子稀薄的过渡金属二卤化碳化物的光学性质有更完整的了解。