Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 3: Graphene: THz, NIR and transport properties (with O/TT)

HL 3.8: Vortrag

Montag, 16. März 2015, 11:15–11:30, ER 270

Ballistic supercurrents in suspended graphene — •Markus Weiss and Christian Schönenberger — Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel

Since the discovery of graphene there have been numerous efforts to use this material as a Josephson weak link between two superconductors. Devices based on oxidized silicon substrates have been produced a few years ago, and have shown bipolar, gate-tuneable supercurrents. The observation of effects are that unique to the Dirac semimetal graphene however has been prevented up to now by the large disorder modulation of the electric potential in graphene on silicon based substrates. For the direct observation of e. g. specular Andreev reflection, the disorder modulation of the Dirac point would have to be smaller that the proximity induced superconducting gap, a regime that cannot be reached in conventional devices. The road to cleaner graphene might go via deposition onto commensurate substrates like hexagonal boron nitride, or the removal of the silicon oxide substrate and suspension of graphene. The latter technique has been perfected in the recent years for devices with normal metal contacts, but turned out to be difficult to realize for superconducting contacts due to incompatibilities of superconducting materials with the fabrication process.

We have developed a device architecture that allows the realization of suspended graphene devices with superconducting contacts, and will show first experimental results, like the ballistic Josephson current through a graphene weak link.