Detection of the chirality of twisted bilayer graphene by the optical absorption

Twisted bilayer graphene possesses intrinsic chirality, which has received less attention among the extensive research conducted on twistronics. In this paper, the optical absorption theory beyond the common linear perturbation is developed with more sophisticated light-electron interactions considered. Numerical calculations based on the theory found that reducing the twisted angle produces a redshift of absorption in the high-frequency range, while increasing absorption strength in the low-frequency domain, which can be further significantly enhanced when applying an interlayer bias. More importantly, the absorption spectroscopy is shown to be an effective way to detect both the chirality and the anisotropy of the twisted bilayer structure.