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Scanning tunneling spectroscopy of epitaxial graphene grown on superconducting rhenium

Vendredi 20 décembre 2013 14:00 - Duree : 1 heure
Lieu : Salle "Remy Lemaire" K 223 (1er étage) bât. K de l’institut Néel/CNRS - 25 rue des martyrs - 38000 Grenoble

Orateur : Soutenance de Thèse de Charlène TONNOIR

Obtaining a transparent interface between graphene and a superconductor has proved to be very challenging and yet essential to induce superconducting correlations in graphene via the so-called proximity effect. This thesis presents a scanning tunneling spectroscopy (STS) study at very low temperature (50 mK) of a novel system achieving such a good electronic contact by the growth of epitaxial graphene on superconducting rhenium. The fabrication and selection of high-crystallographic quality rhenium thin films are briefly explained, followed by the CVD growth process of graphene on various metal substrates and in particular rhenium. STM topographic images reveal a moiré pattern due to the lattice mismatch between graphene and rhenium. We identify this system to a graphene monolayer in strong interaction with the underlying substrate, as corroborated by DFT calculations. STS analyses in the hundreds-meV energy range show a spatial modulation of the density of states (DOS) at the moiré scale, indicating different coupling strengths between ‘hills’ and ‘valleys’ regions. The bulk superconduct ing properties are probed by transport measurements, from which we extract the transition temperature Tc 2K and a superconducting coherence length ξ=18nm. The superconducting gap is extracted from the DOS at 50 mK (Δ=330µeV) and found spatially homogeneous. The superconducting mixed state is studied under magnetic field and an Abrikosov vortex-lattice is uncovered. Finally, a study on various surface morphologies exhibits an anomalous lateral superconducting proximity effect in contradiction with the existing models.

Contact : charlene.tonnoir@cea.fr

Discipline évènement : (Physique)
Entité organisatrice : (INAC/SPSMS)
Nature évènement : (Soutenance de thèse)
Site de l'évènement : Polygone scientifique

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