In recent years, nanoSQUIDs residing on the apex of a quartz tip, suitable for scanning probe microscopy with record size, spin sensitivity, and operating magnetic fields, were developed ^[1]. 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. A limitation which is common to all scanning SQUID systems is their sensitivity to only one component of the magnetic field.

A new device that is fabricated by pulling a quartz tube with a “θ” shaped cross section overcomes this limitation^[2]. This geometry gives rise to two parallel SQUID loops sharing a common branch. Using a focused ion beam, we then etch the tip so that the two SQUID loops become oblique with respect to each other. In this structure, the quantum interference pattern is periodic in both the sum (Φ⁺) and the difference (Φ^-) of the magnetic flux in the two SQUID loops. As a result of the 3D structure, a field in the z direction generates a Φ⁺ signal and a field in the x direction generates a Φ^- signal, allowing tuning the sensitivity of the device to each of the two components of the magnetic field. This SOT can be fabricated as small as 200 nm in diameter and can measure magnetic dipoles with spin sensitivity of less than 5 µ_B/Hz^1/2. An experiment that demonstrates its ability to decouple the different components of the field by measuring the current distribution in a superconducting film is carried out and discussed.

[1] D. Vasyukov, Y. Anahory, L. Embon, D. Halbertal, J. Cuppens, L. Neeman, A. Finkler, Y. Segev, Y. Myasoedov, M. L. Rappaport, M. E. Huber, and E. Zeldov, Nature Nanotech. 8, 639 (2013).

[2] Y. Anahory, J. Reiner, L. Embon, D. Halbertal, A. Yakovenko, Y. Myasoedov, M. L. Rappaport, M. E. Huber, and E. Zeldov , Nano Letters 14, 6481-6487 (2014)