Magnetic mapping of defects in type-II superconductors

TL;DR

This paper develops a theoretical framework for understanding how non-superconducting defects in type-II superconductors induce localized magnetic fields and vortex-antivortex pairs, enabling defect mapping via magnetic field measurements.

Contribution

It provides a new theory explaining defect-induced vortex structures and proposes a method for defect mapping using magnetic field measurements.

Findings

Localized magnetic fields are sensitive to defect shape and position.

External magnetic fields can be used to visualize defects.

Vortex-antivortex pairs are generated by defect perturbations.

Abstract

Recently it was discovered that the non-uniform Meissner current flowing around the pinning sites in the type-II superconductor induces the unconventional vortex-antivortex pairs with the non-quantized magnetic flux [J.-Y. Ge, et al., Nat. Commun. 6, 6573 (2015)]. Here we provide the theory of this phenomenon showing that the vortex-like structures originate from the perturbation of the current streamlines by the non-superconducting defect, which results in the generation of the localized magnetic field. The position and the shape of such vortex dipoles are shown to be very sensitive to the defect form. Thus, applying the external magnetic field or current to the superconductor and using, e.g., the high-resolution scanning Hall microscope to measure the stray magnetic field one can plot the map containing the information about the position of the defects and their shape.