Transport in ropes of carbon nanotubes: Contact barriers and Luttinger liquid theory

In this article we report on the conductance of bundles of single-wall carbon nanotubes as a function of temperature and bias voltage. We focus on the nonlinearity in the IV curves near zero bias, i.e., a pronounced conductance dip. While we observe that all temperature dependent data scale onto a single curve, we also find that the characteristic scaling exponent alpha is widespread between 0.1 and 0.9. This behavior cannot be easily understood within the context of a Luttinger liquid. On the other hand, our data reveal a correlation between alpha and a possible interfacial barrier between the metal contacts and the nanotubes. We point out the importance to gain a better understanding of the interfacial properties between three-dimensional and one-dimensional metals and to include contact effects into the currently existing theory on Luttinger liquid.