Nonlinear Coherent Transport Through Doped Nanotube Junctions

The electronic and phase-coherent transport properties of doped carbon nanotube junctions are studied. It is shown that there are regions of negative differential resistance in the $I-V$ characteristic of small radius metallic tubes, which are not seen for semiconducting tubes. Their origin, as discussed, is different from that of traditional Esaki diodes and resonant tunneling structures. Semiconducting tube characteristics, however, show a region of zero current for nonzero voltages which is asymmetric with respect to the applied bias if there is different doping on each side of the junction.