Degeneracy and repulsion between bands of periodic carbon nanotube junctions

The band structures of the periodic nanotube junctions are investigated by the use of effective mass theory (k.p approximation) and the tight binding model. The periodic junctions are constructed by the periodic introduction of defect pairs, consisting of a pentagonal defect and a heptagonal defect, into the carbon nanotube. We treat the periodic junctions whose unit cell is composed by two kinds of metallic nanotubes. The discussed energy region is near the undoped Fermi level where the channel number is kept to 2, so there are two bands. The degeneracy and repulsion between the two bands are determined only from symmetries.