Observation of Quasisteady Dark Excitons and Gapped State in a Doped Semiconductor

Excitons underpin optical phenomena and can intertwine with correlated electronic states. Unlike bright excitons, dark excitons evade conventional optical detection, and their impact on quasiequilibrium electronic structures remains largely unexplored. Here, using angle-resolved photoemission spectroscopy, we report creating, detecting, and controlling dark excitons in the quasiequilibrium distribution of a doped semiconductor SnSe_{2}. By tuning doping and temperature, we control the excitonic spectral weight and observe a concomitant anisotropic gapped state. Our results broaden the scope of dark excitons beyond ultrafast photoemission studies and highlight a correlation between dark excitons and correlated electrons under quasiequilibrium conditions.