Tunable Optical Rotation in Twisted Black Phosphorus

Black phosphorus (BP) is a typical two-dimensional (2D) layered material with strong in-plane anisotropy and large birefringence, making it possible to manipulate the light field with atomically controlled devices for various optoelectronic and photonic applications-for instance, atomic thickness waveplates. The twist angle in twisted black phosphorus (TBP) can be presented as a new tunable dimension to control BP's optical anisotropy. Here, we report a large and tunable optical rotation effect in TBP, the result of regulating the twist angle and BP thickness. To accurately study the optical rotation and the impact of the twist angle, we developed a new method to prepare TBP. A lab-made polarimeter microscope was used to visualize the optical rotation mapping of TBP. A large polarization-plane rotation (PORA) of 0.49 degrees per atomic layer was observed from an air/BP/SiO2/Si Fabry-Perot cavity at 600 nm, an order of magnitude higher than the PORA of 0.05 degrees per atomic layer reported earlier. For the same thickness, the PORA of TBP can be tuned from 0.48 degrees to 7.75 degrees based on the twist angle from 0 degrees to 90 degrees. Our work provides an efficient method to investigate the anisotropy of 2D materials and their heterojunctions. TBP could help us design novel optical and optoelectronic devices such as tunable nanoscale polarization controllers.

Automated summary

The study reports a tunable optical rotation effect in twisted black phosphorus by regulating the twist angle and thickness. By developing a new preparation method, a higher polarization plane rotation can be observed. Twisted black phosphorus exhibits tunable optical rotation and holds great potential in the research of 2D materials and heterostructures.