Single vortex pinning

The scanning SOT microscope was used to investigate the dynamics of quantized magnetic vortices and their pinning by materials defects in lead films with unprecedented sub-Angstrom sensitivity to vortex displacement. We measured, for the first time, the fundamental dependence of the elementary pinning force of multiple defects on the vortex displacement, revealing a far more complex behavior than has previously been recognized, including striking spring softening and broken-spring depinning, as well as spontaneous hysteretic switching between cellular vortex trajectories. Our results indicate the importance of thermal fluctuations even at 4.2 K and of the vital role of ripples in the pinning potential, giving new insights into the mechanisms of electromagnetic response of superconductors.






  1. Scanning SQUID-on-tip image of Bdc(x,y) showing a single vortex (bright) in a thin Pb film patterned into an 8 µm wide microbridge at T = 4.2 K. The microbridge is in the Meissner state (dark), and the enhanced field outside the edges (bright) is due to the screening of the applied field of 0.3 mT.
  2. Scanning image of Bac(x,y) acquired simultaneously with (a) showing the vortex response to an ac current of Iac = 0.94 mA peak-to-peak (ptp) at 13.3 kHz applied to the microbridge. The Meissner response is visible along the microbridge (Bac = 0, light brown) with positive (negative) Bac outside the left (right) edge due to the field self-induced by Iac.
  3. A zoomed-in image of the measured Bdc(x,y) of a vortex.
  4. (d-f) Numerically derived ∂Bdc/∂x, ∂Bdc/∂y and −xacBdc/∂xyacBdc/∂y with xac = 1.6 nm and yac = −1.9 nm values obtained by a fit to (g).
  5. see (d)
  6. see (d)
  7. Experimentally measured Bac(x,y) of the vortex driven by Iac acquired simultaneously with (c).