Fakultät für Physik, Universität Bielefeld, Universitätsstr. 25, 33615 Bielefeld, Germany.
Institut für Solare Brennstoffe, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
Science. 2017 Sep 22;357(6357):1274-1277. doi: 10.1126/science.aam9598.
Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe, the photoemission events are time ordered with rising initial-state angular momentum. Including intra-atomic electron-electron interaction and angular momentum of the initial localized state yields excellent agreement between theory and experiment. This has required a revision of existing models for solid-state photoemission, and thus, attosecond time-resolved photoemission from solids provides important benchmarks for improved future photoemission models.
飞秒时间分辨光电子能谱表明，人们对固体的光电子发射过程仍未完全理解。在对范德瓦尔斯晶体二硒化钨（WSe）的四个光电子发射通道进行的相对发射延迟测量中，只有考虑到传播延迟和原子内延迟，才能解释这些延迟。原子内延迟取决于初始局域态的角动量，并由原子内相互作用决定。在研究的 WSe 情况下，光电子发射事件随着初始态角动量的增加而有序发生。包含原子内电子-电子相互作用和初始局域态的角动量，使得理论和实验之间达到了极好的一致性。这就需要对现有的固体光电子发射模型进行修正，因此，固体的飞秒时间分辨光电子发射为改进未来光电子发射模型提供了重要的基准。
