Researchers from the University of California, Riverside,have developed a new method to read the valley indices of the dark excitons and trions. The researchers used monolayer (2D) tungsten diselenide (WSe2), a semiconductor with two distinct electronic valleys.The material hosts bright and dark excitons or trions with different spin configurations.

The researchers say that dark excitons and trions in monolayer WSe2 have much longer lifetime and better valley stability than the common bright excitons and trions - which makes them excellent candidates for valleytronic applications. But up until now there was no method to read the valley indices of the dark excitons and trions because their light emission from either valley has exactly the same energy and polarization. By identifying a measurable physical quantity that can distinguish the two valley indices of dark excitons and trions, the team was able to devise a method to read the valley indices.

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