Abstract
In a Josephson junction involving multiband superconductors, competition between interband and interjunction Josephson couplings gives rise to frustration and spatial disjunction of superfluid densities among superconducting condensates1,2,3,4,5,6,7. Such frustrated coupling manifests as the quantum interference of Josephson currents from different tunnelling channels and becomes tunable if channel transparency can be varied5,6,7,8. To explore these unconventional effects in the prototypical s±-wave superconductor FeSe (ref. 9), we use atomic-resolution scanned Josephson tunnelling microscopy10,11,12,13 for condensate-resolved imaging and junction tuning—capabilities unattainable in macroscopic Josephson devices with fixed characteristics. We quantitatively demonstrate frustrated Josephson tunnelling by examining two tunnelling inequalities. The relative transparency of two parallel tunnelling pathways is found tunable, revealing a tendency towards a 0–π transition with decreasing scanned Josephson tunnelling microscopy junction resistance. The simultaneous visualization of both superconducting condensates reveals anticorrelated superfluid modulations, highlighting the role of interband scattering. Our study establishes scanned Josephson tunnelling microscopy as a powerful tool enabling new research frontiers of multicondensate superconductivity.
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Acknowledgements
We thank D. Morr, B. Janko, M. Eskildsen and Y.-T. Hsu for valuable discussions. This work is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (DE-SC0025021 to X.L. for advanced SJTM measurements of unconventional superconductivity); the National Science Foundation, Division of Materials Research (DMR-2236528 to S.R.); startup funding from the University of Notre Dame and the Stavropoulos Center for Complex Quantum Matter (to X.L. for initially setting up the research laboratory); and the Notre Dame Materials Science and Engineering Fellowship (to N.S. and M.T.).
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X.L. conceived of the project. N.S. and M.T. performed the measurements. S.R. provided the FeSe crystals. N.S., M.T. and J.M. performed the data analysis. X.L. wrote the paper with input from all authors. All authors contributed to data interpretation.
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Nature Materials thanks Jia-Xin Yin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Notes 1–5, Figs. 1–12 and references.
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Source Data Fig. 1
Data for plots and SJTM images in Fig. 1.
Source Data Fig. 2
Data for plots and SJTM images in Fig. 2.
Source Data Fig. 3
Data for plots and SJTM images in Fig. 3.
Source Data Fig. 4
Data for plots and SJTM images in Fig. 4.
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Sharma, N., Toole, M., McKenzie, J. et al. Atomic-scale frustrated Josephson coupling and multicondensate visualization in FeSe. Nat. Mater. (2025). https://doi.org/10.1038/s41563-025-02290-y
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DOI: https://doi.org/10.1038/s41563-025-02290-y
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