Strain puts twist on emission of light by 2D semiconductor

Researchers in Japan have succeeded in generating circularly polarized light and controlling its direction without using clunky magnets or very low temperatures. These findings, reported in a paper in Advanced Materials, show promise for the development of materials and devices that can be used in optical quantum information processing.

The light particles known as photons have interesting properties that can be exploited for storing and transporting data, and show tremendous promise for use in quantum computing. This is based on storing information in electrons that then interact with matter to generate data-carrying photons.

The information can be encoded in the direction of an electron’s spin, just as it is stored in the form of 0 and 1 in the ‘bits’ of computers. It can also be stored when electrons occupy ‘valleys’ in the energy bands they move between while they orbit an atom. When these electrons interact with specific light-emitting materials, they generate chiral valley-polarized light, which shows potential for storing large amounts of data.

So far, though, scientists have only managed to generate this type of circularly polarized light using magnets and very cold temperatures, making the technique impractical for widespread use. Taishi Takenobu and Jiang Pu, applied physicists at Nagoya University in Japan, led a team of researchers that have now developed a room-temperature, electrically controlled approach for generating chiral valley-polarized light.

First, the researchers grew a monolayer of semiconducting tungsten disulfide on a sapphire substrate and covered it with an ion-gel film. Then they placed electrodes on either end of this device and applied a small voltage. This generated an electric field and ultimately produced light, including chiral valley-polarized light.

Between -193°C and room temperature, they found that chiral valley-polarized light could only be produced by areas of the device where the sapphire substrate was naturally strained, as a result of the synthetic process. In contrast, strain-free areas could only produce chiral light at much colder temperatures. The researchers therefore concluded that strain plays a crucial role in generating chiral valley-polarized light at room temperatures.

Next, they manufactured a bending stage on which they placed a tungsten disulfide device on a plastic substrate. They used the bending stage to apply strain to their material, driving an electric current in the same direction as the strain and again generating valley-polarized light at room temperature. Applying an electric field to the material switched the chiral light from moving in one direction to moving in the other.

“Our use of strained monolayer semiconductors is the first demonstration of a light-emitting device that can electrically generate and switch right- and left-handed circularly polarized light at room temperature,” says Takenobu. The team now plan to further optimize their device with the aim of developing practical chiral light sources.

This story is adapted from material from Nagoya University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.