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Tunneling spectroscopy of graphene nanodevices proximitized by superconductors - Landry Bretheau - Lundi 14 mai 2018 à 10 h 30

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-12, 4e étage, salle 426

Landry Bretheau, Ecole polytechnique


A normal conductor placed in good contact with a superconductor can inherit its electronic properties. This proximity effect originates from the formation in the conductor of electron-hole states, called Andreev bound states (ABS). Spectroscopic studies of ABS have been performed in just a handful of systems. The unique geometry, electronic structure and high mobility of graphene make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunneling spectroscopy measurements of proximitized graphene, using either aluminum or niobium-nitride as superconductors. The measured energy spectra, which depend on the phase difference between the superconductors, reveal a continuum of ABS. Moreover, we measure the Andreev spectrum as a function of the graphene Fermi energy, showing the influence of scattering in graphene. From the phase dependence of the spectra, we further infer the supercurrent carried by the ABS, thus relating Andreev physics and the Josephson effect. At last, we discuss the origin of phase-dependent features that occur at energies larger than the superconducting gap.

[1] L. Bretheau, J. I.-J. Wang, R. Pisoni, K. Watanabe, T. Taniguchi, P. Jarillo-Herrero, Tunnelling spectroscopy of Andreev states in graphene, Nat. Phys. 13, 756-760 (2017)