Hubert B. Heerschea, Pablo Jarillo-Herrero1, a, Jeroen B. Oostingaa, , Lieven M.K. Vandersypena and Alberto F. Morpurgo, a,
aKavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands Accepted 19 February 2007. by A. Geim. Available online 27 April 2007.
Graphene layers, prepared by mechanical exfoliation, were contacted by superconducting electrodes consisting of a titanium–aluminium bilayer. Quantum hall measurements in the normal state confirmed the single layer nature of the graphene samples. Proximity induced supercurrents were observed in all samples, below 1 K. Using a backgate, the Fermi energy could be swept from valence to conduction band via the Charge neutrality point, demonstrating supercurrents carried by holes and electrons, respectively. Interestingly, a finite supercurrent was also observed at the charge neutrality (or Dirac) point, where the density of carrier states vanishes. Our results demonstrate phase coherence in graphene.
Keywords: A. Graphene; D. Josephson effect; D. Superconductivity