Probing the dark state

Abstract

Physics Excitons, electron-hole pairs held together by Coulomb attraction, can be generated in semiconductors under excitation and greatly influence the material's optoelectronic properties. Although bright excitons are optically active, their dark-state cousins have been more difficult to detect. They do, however, affect the optoelectronic properties through their interaction with light and bright excitons. Madeo et al. developed a pump-probe photoemission technique that is used reveal the spatial, temporal, and spectral dynamics of excitons (see the Perspective by Na and Ye). Demonstrated in two-dimensional monolayer films of tungsten diselenide, the technique could also be applicable to other semiconductor systems hosting excitonic excitations. Science , this issue p. [1199][1]; see also p. [1166][2] [1]: /lookup/doi/10.1126/science.aba1029 [2]: /lookup/doi/10.1126/science.abf0371