  We report low temperature transport measurements on suspended single walled
carbon nanotubes (both individual tubes and ropes). The technique we have
developed, where tubes are soldered on low resistive metallic contacts across a
slit, enables a good characterization of the samples by transmission electron
microscopy. It is possible to obtain individual tubes with a room temperature
resistance smaller than 40 kOhms, which remain metallic down to very low
temperatures. When the contact pads are superconducting, nanotubes exhibit
proximity induced superconductivity with surprisingly large values of
supercurrent. We have also recently observed intrinsic superconductivity in
ropes of single walled carbon nanotubes connected to normal contacts, when the
distance between the normal electrodes is large enough, since otherwise
superconductivity is destroyed by (inverse) proximity effect. These experiments
indicate the presence of attractive interactions in carbon nanotubes which
overcome Coulomb repulsive interactions at low temperature, and enables
investigation of superconductivity in a 1D limit never explored before.
