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Electronic states and transport properties of double-wall carbon nanotubes without impurities are studied in a systematic manner. It is revealed that scattering in the bulk is negligible and the number of channels determines the average conductance. In the case of general incommensurate tubes, separation of degenerated energy levels due to intertube transfer is suppressed in the energy region higher than the Fermi energy but not in the energy region lower than that. Accordingly, in the former case, there are few effects of intertube transfer on the conductance, while in the latter case, separation of degenerated energy levels leads to large reduction of the conductance. It is also found that in some cases antiresonance with edge states in inner tubes causes an anomalous conductance quantization, G = e 2 /π , near the Fermi energy.

Effects of intertube interactions on transport are studied numerically in incommensurate double-wall carbon nanotubes. The intertube transfer at each lattice site oscillates around zero in a complex plane as a function of position in a quasiperiodic manner and therefore cancels each other when being summed up. The cancellation is not perfect in the presence of sharp edges, giving rise to an intertube conductance much smaller than e 2 / ប and determined by the structure at edges. The conductance exhibits a wild and almost irregular oscillation as a function of the length with average and fluctuations independent of the length due to the change of the edge structure.

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