Magnetic flux expulsion in a superconducting wire

TL;DR

This paper investigates how magnetic flux is expelled from superconducting wires, revealing that magnetic field lines move with charge carriers, challenging traditional superconductivity theories.

Contribution

It provides experimental insight into flux expulsion dynamics, linking magnetic field line motion with charge carrier movement, contrasting with conventional theories.

Findings

Magnetic flux is expelled as a surface phenomenon.

Magnetic field lines move with charge carriers, similar to plasma behavior.

Contradicts traditional London-BCS theory of superconductivity.

Abstract

An electric current generates a magnetic field, and magnetic fields cannot exist in the interior of type I superconductors. As a consequence of these two facts, electric currents can only flow near the surface of a type I superconducting wire so that the self-field vanishes in the interior. Here we examine how an electric current flowing through the entire cross-section of a normal conducting wire becomes a surface current when it enters a superconducting portion of the wire. This geometry provides insight into the dynamics of magnetic flux expulsion that is not apparent in the Meissner effect involving expulsion of an externally applied magnetic field. It provides clear evidence that the motion of magnetic field lines in superconductors is intimately tied to the motion of charge carriers, as occurs in classical plasmas (Alfven's theorem) and as proposed in the theory of hole superconductivity \cite{holesc}, in contradiction with the conventional London-BCS theory of superconductivity.