Special CPM Seminar

Scanning SQUID-on-tip microscopy of vortex matter

Yonathan Anahory

Department of Condensed Matter Physics
Weizmann Institute of Science

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. We have developed SOT made of Pb with an effective diameter of 46 nm and flux noise of Φ_n = 50 n Φ₀/Hz^1/2 at 4.2 K that is 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. 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.

We applied this new tool to investigation of static and dynamic behavior of vortices in superconductors with single vortex resolution. By driving ac and dc transport current we can study vortex displacement and vortex potential landscape with sub-atomic precision showing non-trivial features of the pinning potential and complex vortex trajectories. At higher fields we image the flow patterns of moving lattice revealing dynamic instabilities, plastic flow, and ordering.

[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).