Fig. 5: Room-temperature coherence of the directional emission.

Momentum distribution and spatial interference enabled by a cylindrical lens for the directional emission of dark excitons supports an interference pattern b. The destructive interference in the middle of b is due to a π-phase shift between the left and right parts of the light field in a, showing that the directional emission is strongly coherent at room temperature. Momentum distribution and spatial interference for a coherent laser beam. The center of d is brighter than that of c, which is caused by constructive interference. Momentum distribution and spatial interference for incoherent bright exciton emission of monolayer WSe₂ on SiO₂/Si substrate. The intensity profile of f is similar to that of e because the bright exciton lots its valley coherence at room temperature.