Optical materials that can change the refractive index are needed for emerging applications like virtual reality, 3D displays, optical computers, and LiDAR. However large changes in refractive index and fast response are hard to find in common optical materials. We investigated a new class of material based on strong correlations and discovered their large change in refractive index with just ambient light! The change in the index was also fast allowing a switching speed of a few million times per second!

The material we studied is the 1T phase of tantalum disulfide. It is a layered material whose optical properties in the direction across the layers change dramatically with ambient light. Common materials for such tunable applications show a small change in their refractive index and hence require intense lasers to observe appreciable index change. However, thanks to the cooperative behavior of charges in 1T-tantalum disulfide that its refractive index changes on unity order with just ambient light. The charge domains of the material stack differently with illumination resulting in a change in refractive index. In addition, the fast response of the charge domains in this material makes 1T-tantalum disulfide promising for emerging optical applications requiring low power operation, especially on a mobile platform.

More details on this work may be found in the published paper, News release, and News section.