Imaging Excitons in Momentum Space

Optical techniques have provided us with rich information about the exciton – a two-particle photoexcited state in semiconductors and insulators. Yet, they have left a fundamental degree of freedom of the exciton inaccessible – it’s <i>momentum</i>!<br/>In this talk, I will discuss the application of time-resolved photoemission techniques to access the momentum coordinate of excitons in 2D semiconductors, thereby providing us with the formation pathways of momentum-forbidden dark excitons [<i>Science</i> <b>370</b>, 1199 (2020)], an image of the electron around the hole in the exciton, the observation of the long-predicted anomalous dispersion of the exciton-bound electron [<i>Science Advances</i> <b>7</b>, eabg0192 (2021)], the momentum distribution of the exciton-bound hole, and the confinement of the interlayer exciton in a moiré cell [<i>Nature</i> <b>603,</b> 247 (2022)].