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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

Thursday, 31 May 2007
(at 13:30 in room Phy 5.0.20)
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Super carbon: bipolar supercurrents in graphene

Hubert Heersche

Kavli Institute of NanoScience
Delft University of Technology
  The Netherlands  

(From doi: 10.1038/nature05555): Grapheneüa recently discovered form of graphite only one atomic layer thicküconstitutes a new model system in condensed matter physics, because it is the first material in which charge carriers behave as massless chiral relativistic particles. The anomalous quantization of the Hall conductance which is now understood theoretically is one of the experimental signatures of the peculiar transport properties of relativistic electrons in graphene. Other unusual phenomena, like the finite conductivity of order 4e2/h (where e is the electron charge and h is Planck's constant) at the charge neutrality (or Dirac) point have come as a surprise and remain to be explained. Here we experimentally study the Josephson effect in mesoscopic junctions consisting of a graphene layer contacted by two closely spaced superconducting electrodes. The charge density in the graphene layer can be controlled by means of a gate electrode. We observe a supercurrent that, depending on the gate voltage, is carried by either electrons in the conduction band or by holes in the valence band. More importantly, we find that not only the normal state conductance of graphene is finite, but also a finite supercurrent can flow at zero charge density. Our observations shed light on the special role of time reversal symmetry in graphene, and demonstrate phase coherent electronic transport at the Dirac point.

Invited by C. Strunk (Seminar Weiss)

last modified: 2018.10.24 Mi
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