Resonant transmission through finite-sized carbon nanotubes

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Abstract
We have investigated theoretically the conductance through finite-sized carbon nanotubes coupled to featureless leads in the context of standard tight-binding models. Conduction takes place via resonant tunneling, and the resultant spectrum of peaks may be understood in terms of the band structure of the nanotubes. Specific nanotubes display both on- and off-resonance behavior as a function of nanotube length depending upon whether or not the bands cross at a nonzero k value. We have also investigated the approach to the infinite limit in detail, and, in general, find that the finite-size effects can persist out to hundreds of nanometers. Since the manipulation of nanotubes into devices is likely to induce defects, we have investigated their effects on the conduction. The effects of bending and two broad classes of defects, i.e., defect in the absence and/or presence of addimers, were considered. In general, the presence of defects leads both to a reduction and shifting of the resonant peaks at the Fermi level. However, in the infinite limit, low concentrations of defects have only a relatively modest effect on the transport properties. Finally, we have investigated the effects of an externally imposed magnetic field oriented perpendicular to the nanotube axis. The magnetic field shifts the levels, thereby turning on- and off-resonant devices into each other. All of the effects discussed here are testable experimentally.