Conductance in multiwall carbon nanotubes and semiconductor nanowires : evidence of a universal tunneling barrier

Electronic transport in multiwall carbon nanotubes and semiconductor nanowires was compared. In both cases, the non ohmic behavior of the conductance, the so-called zero bias anomaly, shows a temperature dependence that scales with the voltage dependence. This robust scaling law describes the conductance $G(V,T)$ by a single coefficient $\alpha$. A universal behavior as a function of $\alpha$ is found for all samples. Magnetoconductance measurements furthermore show that the conduction regime is weak localization. The observed behavior can be understood in terms of the coulomb blockade theory, providing that a unique tunnel resistance on the order of 2000 $\Omega$ and a Thouless energy of about 40 meV exists for all samples.