A scanning superconducting quantum interference device with single electron spin sensitivity

Abstract

Superconducting quantum interference devices (SQUIDs) can be used to detect weak magnetic fields and have traditionally been the most sensitive magnetometers available. However, because of their relatively large effective size (on the order of 1 µm)1,2,3,4, the devices have so far been unable to achieve the level of sensitivity required to detect the field generated by the spin magnetic moment (μB) of a single electron5,6. Here we show that nanoscale SQUIDs with diameters as small as 46 nm can be fabricated on the apex of a sharp tip. The nano-SQUIDs have an extremely low flux noise of 50 nΦ0 Hz−1/2 and a spin sensitivity of down to 0.38 μB Hz−1/2, which is almost two orders of magnitude better than previous devices2,3,7,8. They can also operate over a wide range of magnetic fields, providing a sensitivity of 0.6 μB Hz−1/2 at 1 T. The unique geometry of our nano-SQUIDs makes them well suited to scanning probe microscopy, and we use the devices to image vortices in a type II superconductor, spaced 120 nm apart, and to record magnetic fields due to alternating currents down to 50 nT.

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Figure 1: SEM images of SOT devices.
Figure 2: Quantum interference patterns and IV characteristics of several SOT devices at 4.2 K.
Figure 3: Flux and spin noise spectra of the SOTs at 4.2 K.
Figure 4: Calculated magnetic flux in the SOT loops versus xy position of a single spin 10 nm below the SQUID plane.
Figure 5: Scanning SOT microscopy images of vortex matter and of magnetic field distribution generated by a.c. current in a Nb film at 4.2 K.

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Acknowledgements

This work was supported by the European Research Council (ERC advanced grant) and by the Minerva Foundation with funding from the Federal German Ministry for Education and Research. Y.A. acknowledges support by the Azrieli Foundation and by the Fonds Québécois de la Recherche sur la Nature et les Technologies. M.H. acknowledges support from the Weston Visiting Professorship programme. E.Z. acknowledges support from the US–Israel Binational Science Foundation (BSF).

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Contributions

D.V. and Y.A. fabricated and measured the SOT devices. Y.A., M.R., Y.M. and L.N. developed the Pb deposition set-up. Y.M., M.R. and D.V. designed and built the Nb evaporator. L.E. designed and constructed the scanning SOT microscope. L.E., D.H. and J.C. carried out the magnetic imaging. D.H. performed numerical analysis and parametric fitting. A.F. and Y.S. contributed to the development of the SOTs and the microscope. M.H. developed the SQUID array readout system. D.V. and E.Z. co-wrote the paper. All authors contributed to the manuscript.

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Correspondence to Denis Vasyukov or Eli Zeldov.

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The authors declare no competing financial interests.

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Vasyukov, D., Anahory, Y., Embon, L. et al. A scanning superconducting quantum interference device with single electron spin sensitivity. Nature Nanotech 8, 639–644 (2013). https://doi.org/10.1038/nnano.2013.169

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