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Printable two-dimensional superconducting monolayers

Abstract

Two-dimensional superconductor (2DSC) monolayers with non-centrosymmetry exhibit unconventional Ising pair superconductivity and an enhanced upper critical field beyond the Pauli paramagnetic limit, driving intense research interest. However, they are often susceptible to structural disorder and environmental oxidation, which destroy electronic coherence and provide technical challenges in the creation of artificial van der Waals heterostructures (vdWHs) for devices. Herein, we report a general and scalable synthesis of highly crystalline 2DSC monolayers via a mild electrochemical exfoliation method using flexible organic ammonium cations solvated with neutral solvent molecules as co-intercalants. Using NbSe2 as a model system, we achieved a high yield (>75%) of large-sized single-crystal monolayers up to 300 µm. The as-fabricated, twisted NbSe2 vdWHs demonstrate high stability, good interfacial properties and a critical current that is modulated by magnetic field when one flux quantum fits to an integer number of moiré cells. Additionally, formulated 2DSC inks can be exploited to fabricate wafer-scale 2D superconducting wire arrays and three-dimensional superconducting composites with desirable morphologies.

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Fig. 1: A general synthesis of 2D superconducting monolayers via cathodic exfoliation.
Fig. 2: Structural and superconductivity characterization of highly crystalline NbSe2 monolayer.
Fig. 3: Josephson junction arrays in van der Waals heterostructures based on electrochemically exfoliated NbSe2.
Fig. 4: Printing the exfoliated NbSe2 flakes.

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Data availability

The datasets generated during the current study are available from the corresponding author on request.

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Acknowledgements

J.Lu acknowledges support from MOE grants (MOE2017-T2-1-056 and MOE2019-T2-2-044) and NRF-CRP Grant (NRFCRP16-2015-02). J.Li acknowledges support from the National Natural Science Foundation of China (21703143). J.D. thanks NRF-CRP16-2015-01 (R284-000-159-281) for support of the 3D printing work. J.H.T. acknowledges support from Agency for Science, Technology and Research (A*STAR) under grant no. 1527000014. This work was supported by the National Research Foundation of Singapore under its Medium-Sized Centre Programme.

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Contributions

J.Lu supervised the project. J.Li, K.S.N. and J.Lu conceived the research and wrote the paper. J.Li and Z.L. performed the cathodic intercalation and exfoliation experiment. P.S. and J.Li. fabricated the Hall bar and vdWHs device. P.S. carried out the low-temperature transport measurement of Hall bar devices and analysed the results. J.Z. and K.V. performed the low-temperature transport measurement of twisted NbSe2 vdWH devices and analysed the results. X.Z. performed the STEM imaging of exfoliated layered sheets and analysis. Z.Q. assisted with the STM imaging of TBA- and TPA-intercalated NbSe2 structures. Z.W. and L.L. fabricated and measured the twisted NbSe2 devices from mechanically exfoliated NbSe2. M.Z. performed inkjet printing of superconducting wires. Y.Z. and W.J. carried out the 3D printing. T.S.H. assisted with the superconductivity measurement of 2D and 3D printing structures. J.Li performed the TEM, AFM and Raman characterization. W.Y., X.H., P.L., H.X., H.Y., C.C., S.J.P., J.D., J.T. and A.H.C.N discussed and commented on the manuscript.

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Correspondence to Kostya S. Novoselov or Jiong Lu.

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Supplementary Figs. 1–36, Table 1 and supporting information.

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Li, J., Song, P., Zhao, J. et al. Printable two-dimensional superconducting monolayers. Nat. Mater. 20, 181–187 (2021). https://doi.org/10.1038/s41563-020-00831-1

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