Metal-to-semiconductor transition in squashed armchair carbon nanotubes

We investigate electronic transport properties of the squashed armchair carbon nanotubes, using tight-binding molecular dynamics and Green's function method. We demonstrate a metal-to-semiconductor transistion while squashing the nanotubes and a general mechanism for such transistion. It is the distinction of the two sublattices in the nanotube that opens an energy gap near the Fermi energy. We show that the transition has to be achieved by a combined effect of breaking of mirror symmetry and bond formation between the flattened faces in the squashed nanotubes.