Deformation-induced anisotropy of absorption spectra in bilayer graphenes

For undeformed bilayer graphenes, the optical absorption spectra demonstrate isotropic features when polarization vectors lie on the graphene plane although the geometric structures, the band structures, and the velocity matrix elements exhibit strong anisotropy. However, deformation could destroy such isotropy owing to the change of the relationship between the energy dispersions and the velocity matrix elements. Thus different spectra are derived when the polarization vector lies along the armchair and zigzag directions for both AA-and AB-stacked bilayer graphenes. The major differences include the number, strength, and frequency of the structures in the absorption spectra. The predicted deformation-induced anisotropy in optical excitations could be verified by experimental measurements.