Quantum transport through carbon nanotubes: Proximity-induced and intrinsic superconductivity

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 $40\mathrm{k}\Omega ,$ 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 enable investigation of superconductivity in a one-dimensional limit never explored before.