Transport in Carbon Nanotubes with Defects

The linear response conductance of a defect free carbon nanotube connected to ideal contacts is approximately 4e(sup 2)/h. In this paper, we first calculate the conductance characteristics of a uniform tube in the presence of an applied bias by assuring different forms of the potential drop across the wire. It is shown that for long tubes, the conduction mechanism involve a only the four non degenerate subands when the electric field drops slowly across the the tube. We then proceed to calculate the transmission and low bias conductance of tubes with defects. Here, we show that a weak uniform disorder in the tube does not cause a dramatic change in the conductance. However the presence of certain substitutional defects, the transmission coefficient versus energy develops a gap and this can cause a dramatic change in the low bias conductance. The effect of coherence is neglected.