  Nano-carbon materials are investigated intensively. In this paper, the
edge-state in nanographene materials with zigzag edges is studied
theoretically. In particular, while the inter-layer interactions are
considered, we prove that edge states exist at the energy of the Dirac point in
the doubly stacked nanographene, and in the case of the infinitely-wide lower
layer case. This property applies both for the A-B and A-C stackings.
