Probing dynamics and pinning of single vortices in superconductors at nanometer scales

TL;DR

This study uses a novel high-resolution microscope to explore vortex dynamics and pinning in superconductors, revealing complex behaviors and the influence of thermal fluctuations at nanometer scales.

Contribution

It introduces a new experimental approach to directly observe vortex behavior at nanometer resolution, uncovering complex pinning phenomena and thermal effects.

Findings

Complex vortex pinning behavior including spring softening and broken-spring depinning

Thermal fluctuations significantly affect vortex dynamics at 4.2 K

Ripples in the pinning potential influence vortex trajectories

Abstract

The dynamics of quantized magnetic vortices and their pinning by materials defects determine electromagnetic properties of superconductors, particularly their ability to carry non-dissipative currents. Despite recent advances in the understanding of the complex physics of vortex matter, the behavior of vortices driven by current through a multi-scale potential of the actual materials defects is still not well understood, mostly due to the scarcity of appropriate experimental tools capable of tracing vortex trajectories on nanometer scales. Using a novel scanning superconducting quantum interference microscope we report here an investigation of controlled dynamics of vortices in lead films with sub-Angstrom spatial resolution and unprecedented sensitivity. 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 magnetic relaxation and electromagnetic response of superconductors.