Investigation of the inter-tube coupling in single-wall nanotube ropes

We present four terminal measurements of resistance as a function of temperature on ropes of single-wall carbon nanotubes. The ropes were intentionally damaged at the surface before the deposition of the metal electrodes. At low temperatures, this damage blocks the transport through the tubes at the surface by localization and the current path changes to lower lying undamaged tubes inside the rope. The pronounced resistance maximum occurring due to this effect is used to extract the inter-tube coupling resistance using a simple resistance network model. The coupling mechanism is argued to be direct tunneling between the tubes.