Induced superconductivity in graphene

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.