Tunable Optical Activity in Twisted Anisotropic Two-Dimensional Materials

Twisted van der Waals structures exhibit a variety ofunusual electricaland optical phenomena and could provide a powerful means for designingnanodevices with tunable chiral properties. However, programming intrinsicchiral properties of the film on the atomic scale remains a greatchallenge due to the limitations of fabrication and measurement techniques.Here, we report a highly tunable large optical activity of twistedanisotropic two-dimensional (2D) materials, including black phosphorus(BP), ReS2, PdSe2, and & alpha;-MoO3, by varying the twist angle between the stacked layers. The chiralitycan be deliberately tailored through the engineering of the symmetry,band structure, and anisotropy of 2D materials, demonstrating thehigh tunability of the chirality. The results show the highest thickness-normalizedellipticity value (13.8 deg & mu;m(-1), twistedReS(2)) and ellipticity value (1581 mdeg, twisted BP) amongthe systems based on 2D materials. It is also shown that the chiropticalresponse exists in an extremely large spectral range from the visibleto the infrared. Furthermore, the twisted ReS2 enabledspin-selective control of the information transformation. These resultsshow that highly controllable chirality in twisted 2D anisotropicmaterials has considerable potential in on-chip polarization optics,nano-optoelectronics, and biology.

Automated summary

Twisted van der Waals structures exhibit tunable chiral properties in twisted anisotropic two-dimensional materials, such as black phosphorus, ReS2, PdSe2, and α-MoO3. The chirality can be tailored through engineering the symmetry, band structure, and anisotropy of these materials. The highest thickness-normalized ellipticity value and ellipticity value among 2D material systems have been achieved. The results also show that the chiroptical response exists in a wide spectral range and enable spin-selective control of information transformation.