Two mechanisms that drive metal-to-semiconductor transitions in single-walled
carbon nanotubes are theoretically analyzed through a simple tight-binding
model. By considering simple structural trends, the results demonstrate that
metal-to-semiconductor transitions can be induced more readily in metallic
zigzag nanotubes than in armchair nanotubes. Furthermore, it is shown that both
mechanisms have the effect of making the two originally equivalent sublattices
physically distinguishable.Comment: 4 pages, 4 figure