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The tunneling conductance of junctions between a highly disordered carbon nanotube
and a metallic electrode shows a characteristic zero-bias anomaly due to electron-electron interactions.
Due to the high resistivity of the nanotube material, around 50 kOhm/micron, the field diffusion is rather
slow. In wide enough contacts, the finite size of the junctions comes into play, and the observed anomaly
can be described using theoretical model for 1D tunnel junctions.
The disorder-enhanced anomaly is well known in metallic systems, where the anomaly typically
is small, only a few percent. In our disordered nanotubes we observe a much larger anomaly, and this opens a possibility
to study the phenomenon in non-perturbative regime. The temperature dependence of the conductivity in our samples
is found to be in good agreement with recent theoretical work (Rollbühler and Grabert, PRL 87, 126804 (2001);
Mischenko et al. PRL 87, 246801 (2001)). The tunneling conductance is roughly given by G ~ exp(-(T/T0)1/2).
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The disordered nanotubes are not suitable for fabrication of SET transistors, because the
high resistivity of the nanotube suppresses the SET oscillations. The Coulomb blockade occurs in a single junction,
isolated by the high resistance of the nanotube, irrespective of the existence of the other junction.
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