Researchers from the University of California, Riverside, has observed light emission intervalley transmissions. The researchers say that this light emission can be used to read valley information from Valleytronics devices in the future.

The researhers observed the phenomenon in monolayer tungsten diselenide (WSe2) - a promising valleytronic material that possesses two valleys with opposite dynamic characteristics in the band structure, and can interact strongly with light.

The researchers explain that when 2D WSe2 absorbs a photon, a bound electron can be freed in a valley, leaving behind an electron vacancy, or "hole". The electron and hole in the same valley can attract each other to form a bound state called an intravalley exciton. An electron and a hole in opposite valleys can also form an exciton, called an intervalley exciton - a novel component in valleytronics. But the law of momentum conservation forbids an electron and a hole in opposite valleys to recombine directly. As a result, intervalley excitons are hidden in the optical spectrum.

The researchers now managed to observe light emission from intervalley excitons in monolayer WSe2. The team found that although the intervalley excitons are intrinsically dark, they can emit a significant amount of light with the assistance of either defects or lattice vibrations in the material.