Abstract

The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a two-dimensional system. A superconductor (SC) contacting these states can provide correlations of the quasiparticles in the dissipationless edge states. Here we fabricated highly transparent and nanometre-scale SC junctions to graphene. We demonstrate that the QH edge states can couple via superconducting correlations through the SC electrode narrower than the superconducting coherence length. We observe that the chemical potential of the edge state exhibits a sign reversal across the SC electrode. This provides direct evidence of conversion of the incoming electron to the outgoing hole along the chiral edge state, termed crossed Andreev conversion (CAC). We show that CAC can successfully describe the temperature, bias and SC electrode width dependences. This hybrid SC/QH system could provide a novel route to create isolated non-Abelian anyonic zero modes, in resonance with the chiral edge states.

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Acknowledgements

We thank S.-C. Zhang, B. Halperin and J. Alicea for fruitful discussions. The major experimental work, including sample preparation and measurement, is supported by DOE (DE-SC0012260). The Harvard collaboration was supported by the Science and Technology Center for Integrated Quantum Materials, NSF Grant No. DMR-1231319. G.-H.L. acknowledges support from the Nano Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2012M3A7B4049966). P.K. acknowledges partial support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4543 and ARO (W911NF-14-1-0638). K.-F.H. is supported by NSF (EFRI 2-DARE 1542807). A.Y. acknowledges support from the US DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award de-sc0001819. D.S.W. acknowledges the support from the National Science Foundation Graduate Research Fellowship under Grant No. DGE1144152. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan and JSPS KAKENHI Grant Numbers JP26248061, JP15K21722 and JP25106006. A portion of this work was performed at the Center for Nanoscale Systems at Harvard, supported in part by an NSF NNIN award ECS-00335765.

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Author notes

    • Sean Hart

    Present address: Department of Physics, Stanford University, Stanford, California 94305, USA.

Affiliations

  1. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

    • Gil-Ho Lee
    • , Ko-Fan Huang
    • , Di S. Wei
    • , Sean Hart
    • , Amir Yacoby
    •  & Philip Kim
  2. Department of Electrical Engineering, M.I.T., Cambridge, Massachusetts 02138, USA

    • Dmitri K. Efetov
  3. ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain

    • Dmitri K. Efetov
  4. National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan

    • Takashi Taniguchi
    •  & Kenji Watanabe

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Contributions

G.-H.L. and P.K. conceived the idea and designed the project. P.K. supervised the project. G.-H.L., K.-F.H. and S.H. fabricated the devices. T.T. and K.W. provided single crystals of hBN. G.-H.L. and D.S.W. performed the measurements. G.-H.L. and P.K. analysed the data and wrote the manuscript. G.-H.L., K.-F.H., D.K.E., D.S.W., S.H., A.Y. and P.K. contributed to the discussion.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Philip Kim.

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DOI

https://doi.org/10.1038/nphys4084

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