Yonathan Anahory, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel
NanoSQUIDs residing on the apex of a quartz tip, suitable for scanning probe microscopy with record size, spin sensitivity, and operating magnetic fields, are presented. The SQUID-on-tip (SOT) is fabricated by pulling a quartz tube into a sharp pipette, followed by three thermal evaporation steps of a thin superconducting film onto the sides and the apex of the pipette. This self-aligned fabrication method requires no additional lithographic processing or etching. An aluminum SOT of 200 nm diameter, operating at 300 mK, showed flux sensitivity of Φn = 1.8 µΦ0/Hz1/2 and spin sensitivity of Sn = 65 µB/Hz1/2 . We have developed SOTs made of Nb and Pb that have the advantage of operating at 4.2 K. The best performance was achieved with a Pb SOT with an effective diameter of 46 nm with Φn = 0.05 μΦ0/Hz1/2 at 4.2 K that was operational up to unprecedented high fields of 1 T. This corresponds to a spin sensitivity of Sn = 0.34 μB/Hz1/2, which is more than one order of magnitude more sensitive than that of any other SQUID to date. This extraordinary sensitivity, combined with the ability of the SQUID-on-tip to scan the sample within a few nm from the sample surface, opens the pathway to direct imaging and investigation of magnetic moments as small as those of a single electron spin. I will also present a SOT that can measure both in-plane and out-of-plane component of the magnetic field.
A. Finkler, Y. Segev, Y. Myasoedov, M. L. Rappaport, L. Neeman, D. Vasyukov, E. Zeldov, M. E. Huber, J. Martin and A. Yacoby, Nano Lett. 10, 1046 (2010)
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