Electronic properties of bilayer AA-stacked zigzag nanographene ribbons

First-principles calculations within the generalized gradient approximation are employed to calculate the electronic properties of the bilayer AA-stacked zigzag nanographene ribbon. The AFM-AFM configuration (antiferromagnetic and antiferromagnetic configurations for the intralayer and interlayer spin arrangements, respectively) is predicted to be the most stable system. The interlayer interactions alter the band structure such as the modulation of energy dispersions, the generation of new band-edge states, and the state degeneracy. The energy gap is inversely proportional to the ribbon width. As compared with the monolayer zigzag nanographene ribbon, the density of states exhibits more asymmetric peaks, and some peaks at low energy are enhanced due to the state degeneracy. These predicted results can be identified by scanning tunneling spectroscopy (STS) or the measurements of optical spectra.