When circularly polarized light is applied to a single-layer transition metal dalcogenide, two types of excitons that rotate clockwise or counterclockwise can be generated.The concept of using this exciton valley, which is like a valley of energy, in correspondence with 2 and 0 of digital information processing is called "optovaletronics", and in recent years it has been said that high-speed and energy-saving optoelectronic devices can be realized. It is attracting worldwide attention.

　In order to realize opt-valleytronics, it is necessary to maintain the state of the valley for a sufficient time, but in reality it is lost in a very short time and the mechanism is unknown, which is a big problem to be solved. rice field.

　In this study, using tungsten diserenede, which is a typical transition metal dichalcogenide, as a model, the retention time of the valley state becomes shorter as the temperature rises under low temperature conditions, and these properties are mainly the center of gravity of excitons. We have identified a mechanism that depends on the momentum and the density of doped electrons.Then, based on the understanding of this mechanism, when a structure was created in which the momentum of excitons and the density of doped electrons were controlled in the direction of extending the retention time of the valley state, it was possible to enhance it as expected. ..

　This result clarifies the mechanism by which the valley state of excitons once created is lost, and also provides a material engineering guideline for controlling the valley state to some extent. It is expected to lead to realization.

Paper information:[Nature Communications] Evidence for line width and carrier screening effects on excitonic valley relaxation in 2D semiconductors