The remarkable features of the local density of states at a single n-membered ring defect (n = 4, 5, 7, or 8) in mono-layered graphite were described. On the basis of the n-fold rotational symmetry at the center of the n-membered ring, the wave functions and spectra of these systems were classified into n types of component; according to the nature of the rotational symmetry group. By taking account of this symmetry, the local density of states was concluded to be broadened energy levels of the corresponding isolated n-membered ring molecule. The n-membered ring defect, in the large-n limit, could be considered to be a screw dislocation. The value of its local density of states approached zero as the inverse of the logarithm of the energy at the band edges and at the band center.

R.Tamura, K.Akagi, M.Tsukada, S.Itoh, S.Ihara: Physical Review B, 1997, 56[3], 1404-11