Entry of magnetic flux into a magnetically shielded type-II superconductor filament

TL;DR

This paper investigates how magnetic flux enters a type-II superconductor filament with a soft-magnet sheath under external magnetic fields, analyzing critical fields and vortex nucleation using the London approximation.

Contribution

It provides an exact solution for vortex configurations and reveals the influence of magnet sheath parameters on vortex nucleation and flux penetration.

Findings

Critical fields depend on magnet sheath properties.

The Bean-Livingston barrier is significantly affected by the sheath.

Vortex nucleation is modulated by the superconductor-magnet interface.

Abstract

In the framework of the London approximation the magnetic flux penetration into a type-II superconductor filament surrounded by a soft-magnet sheath and exposed to a transverse external magnetic field is studied. The lower transverse critical field as well as the critical field and the critical current of the first vortex nucleation at the superconductor/magnet interface are calculated on the basis of an exact solution for a vortex of arbitrary plane configuration. The Bean-Livingston barrier against the vortex nucleation is shown to strongly depend on the magnet sheath parameters.