Editing Quantum wire (section)

== Carbon nanotubes ==
[[file:Carbon nanotube bands.gif|thumb|Band structures computed using [[tight binding]] approximation for (6,0) CNT ([[zigzag]], [[metal]]lic), (10,2) CNT (semiconducting) and (10,10) CNT ([[armchair nanotube|armchair]], metallic)]]

The [[carbon nanotube]] is an example of a quantum wire. A metallic single-walled carbon nanotube that is sufficiently short to exhibit no internal scattering ([[ballistic transport]]) has a conductance that approaches two times the [[conductance quantum]], <math>2e^2/h</math>. The factor of two arises because carbon nanotubes have two spatial channels.<ref>{{cite book|last1=Dresselhaus|first1=M. S.|author-link1=Mildred Dresselhaus|last2=Dresselhaus|first2=G.|last3=Avouris|first3=Ph.|author-link3=Phaedon Avouris|title=Carbon nanotubes: synthesis, structure, properties, and applications|publisher= Springer|date= 2001|ISBN=3-540-41086-4}}</ref>

The structure of a nanotube strongly affects its electrical properties. For a given (''n'',''m'') nanotube, if ''n'' = ''m'', the nanotube is metallic; if ''n'' − ''m'' is a multiple of 3, then the nanotube is semiconducting with a very small band gap, otherwise the nanotube is a moderate [[semiconductor]]. Thus all armchair (''n'' = ''m'') nanotubes are metallic, and nanotubes (6,4), (9,1), etc. are semiconducting.<ref name="Curvature">{{cite journal|first1=X.|last1=Lu|first2=Z.|title=Curved Pi-Conjugation, Aromaticity, and the Related Chemistry of Small Fullerenes (C<sub>60</sub>) and Single-Walled Carbon Nanotubes|journal=[[Chemical Reviews]]|volume=105|pages=3643–3696|year=2005|doi=10.1021/cr030093d|issue=10|last2=Chen|pmid=16218563}}</ref>