Optical absorption spectra in ABC-stacked graphene superlattice

The band structures in ABC-stacked graphene superlattice include linear and parabolic bands with and without degeneracy. Two of the three-pair band-edge states are located at the symmetric points of the first Brillouin zone, while the other is near the points. These band-edge states can induce prominent structures in the joint density of states (DJ) which exhibits one peak with two shoulders at middle frequency and one peak at low frequency. The square of the velocity matrix element has the greatest values at the symmetric points. It makes the optical absorption spectra (A(ω)) not to fully reflect the DJ structures. The middle-frequency structures become two sharper peaks and the low-frequency peak disappears in A(ω), and A(ω) for the parallel polarization is much stronger than that for the vertical polarization. The spectra contrast sharply with those of AA- and AB-stacked systems, and some of the calculated results could be verified the experimental measurements.

► The special band structures are caused by the unique stacking.
► Not all of the band-edge states of the middle energy are located at the M points.
► Both DJ and |V(k)|2 must be strong to make prominent structures in the spectra.
► The absorption spectra differ much from the spectra of AA- and AB-stacked systems.