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Jeudi 10 Janvier 2013, 14h
Amphi Howleck, Esc C, 1ème etage
The superconducting proximity effect in graphene : from zero field to the Quantum Hall regime
Sophie Gueron
Laboratoire de Physique des Solides UMR 8502 Université Paris Sud, 91405 Orsay cedex, France
The superconducting proximity effect, in which a superconducting contact induces pair correlations in a non superconducting material, is a way to probe the quantum phase coherence of mesoscopic conductors. It also enables the investigation of intrinsic properties of the conductors, such as the number and transmission of its conduction channels, its magnetic properties, etc…
In the case of graphene, the special band structure, in which two Dirac cones touch at half filling, could lead to a special type of Andreev reflection at the graphene/superconductor boundary. Graphene is also an ideal material in which to realize a proximity effect in the Quantum Hall regime, if superconductors can be used which remain superconducting at the high fields required.
After an introduction on the mesoscopic superconducting proximity effect, I will present our recent results on graphene Josephson junctions : we have found that a supercurrent flows through a Superconducting/Graphene/Superconducting junctions with Nb electrodes even through a very long graphene distance of 1.m, more than 3 times the length previously reported. This supercurrent disappears in the vicinity of the Dirac point, indicating a strong sensitivity of the transmission of Andreev pairs to the formation of charge puddles with size greater than the superconducting coherence length.
We also present data on similar size graphene samples with superconducting electrodes with a high critical field (more than 7 Tesla) for which the properties of the normal state are dominated by quantum Hall physics. Whereas the behavior of the supercurrent is similar to the Nb/Graphene/Nb system in zero field, new features are observed in the high field quantum Hall regime.