Fabrication and characterization of nanoSQUID-on-tip sensors with nΦ₀/√Hz magnetic flux sensitivity

nanoSQUID-on-tip (nSOT) sensors offer a versatile platform for nanoscale magnetic imaging and spectroscopy due to their lithography-free fabrication, sub-micron loop size, and easy integration into scanned probe systems [1]. We have recently improved the state-of-the-art of nSOT magnetometry by reaching a flux noise down to a few nΦ₀/√Hz [2] and have thoroughly characterized the electromagnetic behavior of such ultra-sensitive sensors. In this talk, I will present our high-yield nSOT fabrication with optimized superconducting film quality enabled through precise control of the self-aligned thermal evaporation process. I will also explore the interplay between the electromagnetic environment of the tip apex and the readout circuit in shaping the flux-to-voltage transducer response. Specifically, ultrahigh magnetic sensitivity was achieved by stabilizing the nSOT sensor in a negative differential conductance regime against electromagnetic and thermal perturbations. Our findings open new venues for extending this sensitive regime into lower fields and temperatures via impedance engineering.

[1] A. Finkler, Y. Segev, Y. Myasoedov, et al., Nano Letters 10, 1046 (2010).

[2] E. Redekop, C. Zhang, H. Park, et al., arXiv:2405.10269 (to appear in Nature).