Tunnelling spectroscopy of Andreev states in graphene
Author(s)Bretheau, Landry; Wang, Joel I-Jan; Pisoni, Riccardo; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo; ... Show more Show less
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A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties1,2. This proximity effect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states3-8. Spectroscopic studies of Andreev states have been performed in just a handful of systems9-13. The unique geometry, electronic structure and high mobility of graphene14,15 make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity effect in superconductor-graphene- superconductorjunctions.Themeasuredenergyspectra,which depend on the phase difference between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between different mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent-phase relation in a tunnelling experiment,thusestablishingtheconnectionbetweenAndreev physics at finite energy and the Josephson effect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials 16-18 .
DepartmentMassachusetts Institute of Technology. Department of Physics
Bretheau, Landry et al. “Tunnelling Spectroscopy of Andreev States in Graphene.” Nature Physics 13, 8 (May 2017): 756–760 © 2017 Macmillan Publishers Limited, part of Springer Nature
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