Quantum transport through short semiconducting nanotubes: A complex band structure analysis

With a recently developed ab initio nonequilibrium Green's function formalism, we have examined the problem of quantum transport through prototypical, short, semiconducting nanotube devices. Metallic behavior is predicted for very short nanotubes, which crosses over to semiconducting behavior as the tube length is increased. This behavior finds its origins in the evanescent modes that are present in these finite-sized systems, which cannot be ignored. A complex band structure analysis makes the contributions of these modes particularly transparent.