Ferromagnetism, adatom effect, and edge reconstruction induced by Klein boundary in graphene nanoribbons.

The electronic structure and magnetic characteristics of Klein graphene nanoribbons (KGNRs), as observed by Suenaga and Koshino [K. Suenaga and M. Koshino, Nature 468, 1088 (2010)], are investigated using first-principles calculations. We find three new characteristics induced by the Klein boundary. First, the localized edge states in the KGNRs have a ferromagnetic coupling rather than the antiferromagnetic coupling of the zigzag graphene nanoribbons (ZGNRs). Lieb's theorem is no longer applicable in the KGNRs. Second, the marginal single carbon adatom of the ZGNRs can destroy the edge states nearby. The edge states can recover if the length of the zigzag chains is equal to or greater than five times that of the lattice constant. Finally, we show that the pentagon-heptagon edge can be induced from the Klein boundary. [ABSTRACT FROM AUTHOR]