Session L6 - Superconducting Junctions and Proximity Effect.
INVITED session, Tuesday afternoon, March 13
Room 608, Washington State Convention Center
Carbon nanotubes (CN) consist in a rolled-up graphene layer (Single Walled NanoTube, SWNT) of a few micrometers long, which can be assembled in crystalline ropes of typically 100 tubes. They can either form nested structures, called MultiWalled carbon Nanotubes (MWNT). Depending on its geometry, a SWNT can be either semiconducting or conducting with at most two conduction channels. In such a system, strong electronic correlations lead to a breakdown of the Fermi Liquid state, with collective low energy excitations and no long range order (Lutttinger Liquid). Such indications of LL behavior were recently reported above 10K with an extrapolation to an insulating state at low temperature. However, due to Coulomb blockade, the low temperature and voltage regime could not be explored.
In contrast, we have developed a technique in which measuring pads are connected through low contact resistance to suspended nanotubes. We have performed measurements down to 50 mK on superconductor-CN-superconductor junctions, where the superconductor could be either Au/Ta or Au/Re, and the CN either SWNT, ropes or MWNT. In each case, we observed a transition to a superconducting state with typical transition temperature close to the transition temperature of the contacts. A Josephson effect was observed with unexpected high values of the critical current, raising the question of the existence of intrinsic superconductivity in CN. We recently observed intrinsic superconductivity in sufficiently long ropes of SWNT connected to normal contacts.