Imaging individual superconducting vortices in amorphous Mo_0.8Si_0.2 by scanning SQUID-on-tip

Understanding vortex pinning and dynamics in superconductors is crucial for the design of devices carrying non-dissipative currents. Here, we use a scanning nanometer-scale superconducting quantum interference device (nanoSQUID) [1,2] to image individual vortices in a Mo0.8Si0.2 amorphous thin film. MoxSi1-x has recently gained prominence in sensitive superconducting single-photon detectors due to its ease of growth, homogeneity, and high critical temperature (~7 K) [3]. The high flux sensitivity and spatial resolution of our scanning nanoSQUID-on-tip allow us to study the behaviour of individual vortices in the presence of applied field and current. In particular, we investigate flux pinning by driving vortices through Lorentz forces exerted by applied currents [4,5], hopping between pinning sites, and the expulsion of magnetic flux upon lowering the applied magnetic field.

[1] Finkler et al, Nano Lett 10 (2010) 1046; Vasyukov et al, Nat Nanotechnol 8 (2013) 639.
[2] Vasyukov et al, Nano Lett 18 (2018) 964
[3] Caloz et al, Appl Phys Lett 110 (2017) 083106
[4] Embon et al, Sci Rep 5 (2015) 7598
[5] Jelic et al., Nat. Commun. 8, 85 (2017).