Octagonal defect lines in graphene structures

We study graphene nanoribbons and carbon nanotubes containing defect lines built of octagonal rings. All the calculations are performed within the π-electron tight binding approximation, taking into account electron interaction effects by means of the Hubbard model. Octagonal defect lines are the source of state localization at Fermi energy and in some cases may lead to spontaneous magnetization. We show that the localization is due to the zigzag nature of the edges of defect lines.