Vortex Penetration into a Type II Superconductor due to a Mesoscopic External Current

TL;DR

This paper uses London theory to analyze how external currents near a superconductor's surface influence vortex entry, revealing that local magnetic fields can be increased before vortices penetrate, especially in anisotropic materials.

Contribution

It introduces a model for curved vortex behavior near surfaces under external currents, predicting vortex entry thresholds considering surface defects and anisotropy.

Findings

Larger local magnetic fields can be applied before vortex entry.

Surface defects facilitate vortex penetration despite the Bean-Livingston barrier.

Anisotropic superconductors can enhance this effect.

Abstract

Applying the London theory we study curved vortices produced by an external current near and parallel to the surface of a type II superconductor. By minimizing the energy functional we find the contour describing the hard core of the flux line, and predict the threshold current for entrance of the first vortex. We assume that the vortex entrance is allowed due to surface defects, despite the Bean-Livingston barrier. Compared to the usual situation with a homogeneous magnetic field, the main effect of the present geometry is that larger magnetic fields can be applied locally before vortices enter the superconducting sample. It is argued that this effect can be further enhanced in anisotropic superconductors.