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Title: Tunnelling spectroscopy of Andreev states in graphene

Abstract

A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties. This proximity effect microscopically originates from the formation in the conductor of entangled electron–hole states, called Andreev states. Spectroscopic studies of Andreev states 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. In this paper, we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity effect in superconductor–graphene–superconductor junctions. The measured energy spectra, 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, thus establishing the connection between Andreev physics at finite energy and the Josephson effect. Finally, this work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials.

Authors:
 [1];  [1];  [1]; ORCiD logo [2];  [2];  [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Physics
  2. National Inst. for Materials Science (NIMS), Tsukuba (Japan)
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); Gordon and Betty Moore Foundation (United States); Taiwan Merit Scholarship
OSTI Identifier:
1473905
Grant/Contract Number:  
SC0001819; DMR-0819762; ECS-0335765; GBMF4541; TMS-094-1-A-001
Resource Type:
Accepted Manuscript
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 13; Journal Issue: 8; Journal ID: ISSN 1745-2473
Publisher:
Nature Publishing Group (NPG)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; electronic properties and devices; electronic properties and materials; superconducting devices; superconducting properties and materials

Citation Formats

Bretheau, Landry, Wang, Joel I-Jan, Pisoni, Riccardo, Watanabe, Kenji, Taniguchi, Takashi, and Jarillo-Herrero, Pablo. Tunnelling spectroscopy of Andreev states in graphene. United States: N. p., 2017. Web. doi:10.1038/NPHYS4110.
Bretheau, Landry, Wang, Joel I-Jan, Pisoni, Riccardo, Watanabe, Kenji, Taniguchi, Takashi, & Jarillo-Herrero, Pablo. Tunnelling spectroscopy of Andreev states in graphene. United States. doi:10.1038/NPHYS4110.
Bretheau, Landry, Wang, Joel I-Jan, Pisoni, Riccardo, Watanabe, Kenji, Taniguchi, Takashi, and Jarillo-Herrero, Pablo. Mon . "Tunnelling spectroscopy of Andreev states in graphene". United States. doi:10.1038/NPHYS4110. https://www.osti.gov/servlets/purl/1473905.
@article{osti_1473905,
title = {Tunnelling spectroscopy of Andreev states in graphene},
author = {Bretheau, Landry and Wang, Joel I-Jan and Pisoni, Riccardo and Watanabe, Kenji and Taniguchi, Takashi and Jarillo-Herrero, Pablo},
abstractNote = {A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties. This proximity effect microscopically originates from the formation in the conductor of entangled electron–hole states, called Andreev states. Spectroscopic studies of Andreev states 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. In this paper, we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity effect in superconductor–graphene–superconductor junctions. The measured energy spectra, 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, thus establishing the connection between Andreev physics at finite energy and the Josephson effect. Finally, this work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials.},
doi = {10.1038/NPHYS4110},
journal = {Nature Physics},
number = 8,
volume = 13,
place = {United States},
year = {2017},
month = {5}
}

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Works referenced in this record:

Electronic transport in two-dimensional graphene
journal, May 2011

  • Das Sarma, S.; Adam, Shaffique; Hwang, E. H.
  • Reviews of Modern Physics, Vol. 83, Issue 2, p. 407-470
  • DOI: 10.1103/RevModPhys.83.407

The electronic properties of graphene
journal, January 2009

  • Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.
  • Reviews of Modern Physics, Vol. 81, Issue 1, p. 109-162
  • DOI: 10.1103/RevModPhys.81.109