Intertube coupling in ropes of single-wall carbon nanotubes

We investigate the coupling between individual tubes in a rope of single-wa ll carbon nanotubes using four probe resistance measurements. By introducin g defects through the controlled sputtering of the rope we generate a stron g nonmonotonic temperature dependence of the four terminal resistance. This behavior reflects the interplay between localization in the intentionally damaged tubes and coupling to undamaged tubes in the same rope. Using a sim ple model we obtain the coherence length and the coupling. resistance. The coupling mechanism is argued to involve direct tunneling between tubes.