Effect of topological defects in graphite

Abstract

The simplest topological defect in a graphite sheet can be introduced by switching one bond with the movement of two carbon atoms, which transforms four hexagons to two pentagons and two heptagons. Putting the topological defects periodically in a graphite sheet, we study how the electronic state changes based on the tight binding model. Depending on the combination of geometrical parameters which specify the arrangement of the defects, we find that the electronic states can be classified into the zero-gap semiconducting, semimetallic and metallic cases. The localized charge density states at the defect sites emerge just above the Fermi level. Curious states having a flat band at the Fermi level appear in some particular geometrical arrangements of the defects. In addition, we propose to design a series of graphitic polymers with a flat lowest-unoccupied band.