Superconducting QUantum Interference Devices (SQUID) are traditionally the most sensitive device for measuring magnetic field. However, because of their relatively large sizes (> 1 µm²) and limitations on reducing the device-to-sample distance to submicron range, SQUIDs were not used so far for magnetic imaging at the nanoscale. We have developed nanoSQUIDs-on-tip (SOT) made of Pb with an effective diameter of down to 46 nm and flux noise of Φ_n = 50 nΦ₀/Hz^1/2 at 4.2 K that are operational up to unprecedented high fields of 1 T [1]. The corresponding spin sensitivity of the device is S_n = 0.38 μ_B/Hz^1/2, which is about two orders of magnitude more sensitive than any other SQUID to date.

Using this novel technique, we have carried out study of dynamics of single vortices in superconductors subjected to ac and dc drive. The outstanding sensitivity of the SOT allows probing vortex displacements as low as 10 pm [2]. Thus we were able, for the first time, to measure the structure of disorder-induced vortex pinning potential as a function of the position with sub-nanometer resolution. The study finds rich internal structure of the pinning potential and of the restoring force, and reveals unexpected phenomena such as softening of the restoring force, nontrivial vortex trajectories within a single potential well, pronounced anisotropy, and abrupt depinning. The results shed new light on the importance of multi-scale random disorder on vortex dynamics and thermal fluctuations even at 4.2K.

[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] L. Embon, Y.Anahory, A. Suhov, D. Halbertal, J. Cuppens, A. Yakovenko, A. Uri, Y. Myasoedov, M.L. Rapparport, M.E. Huber, A. Gurevich and E. Zeldov, Scientific Reports (in press)