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 metallic contacts across a slit enables a good characterization of the samples by transmission electronic microscopy.
It is possible to obtain individual tubes which remain metallic down to very low temperatures with only a small increase of resistance between room temperature and 1K. When the contact pads are superconducting, nanotubes exhibit proximity induced superconductivity with surprising large values of supercurrent. It has also been recently possible to observe intrinsic superconductivity in ropes of single walled carbon nanotubes connected to normal contacts provided that the distance between the normal electrodes is large enough, 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 opens the investigation of superconductivity in a 1D limit never explored before.