CARBON NANOTUBES AS LONG BALLISTIC CONDUCTORS

Early theoretical work on single-walled carbon nanotubes(1-3) predicte d that a special achiral subset of these structures known as armchair nanotubes(3) should be metallic. Tans et al.(4) have recently confirme d these predictions experimentally and also showed directly that coher ent electron transport can be maintained through these nanowires up to distances of at least 140 nm. But single-walled armchair nanotubes ar e one-dimensional conductors with only two open conduction channels (e nergy subbands in a laterally confined system that cross the Fermi lev el)(1-3). Hence, with increasing length, their conduction electrons ul timately become localize(5) owing to residual disorder in the tube whi ch is inevitably produced by interactions between the tube and its env ironment. We present here calculations which show, however, that unlik e normal metallic wires, conduction electrons in armchair nanotubes ex perience an effective disorder averaged over the tube's circumference, leading to electron mean free paths that increase with nanotube diame ter. This increase should result in exceptional ballistic transport pr operties and localization lengths of 10 mu m or more for tubes with th e diameters that are typically produced experimentally(6).