Vortex deformation close to a pinning center

Abstract

Vortex–pinning effect plays an important role in both scientific and technological disciplines of superconductivity. However, little is known about the detailed evolution of a vortex approaching a pinning center. Using scanning Hall probe microscopy, we have directly visualized, at a microscopic level, the interaction of a single quantum vortex with pinning centers. When few adjacent pinning centers are present, the vortex can be trapped by one of them while the interaction of the vortex with the adjacent pinning centers can be tuned by varying superconducting characteristic lengths with temperature. It is found that when the vortex size is comparable to the distance between two pinning centers, the vortex deforms along the line connecting the pinning centers and the magnetic flux spreads by embracing both pinning centers, thus generating a magnetic dipole. In contrast, a vortex located on an isolated pinning center preserves its round shape up to temperatures close to the critical temperature. The experimental data are in a good agreement with theoretical simulations based on the time-dependent Ginzburg-Landau approach.