Electrodynamics of spin currents in superconductors

TL;DR

This paper develops an extended electrodynamic model for superconductors that predicts the existence of spin currents and charge expulsion, providing a framework to quantify these effects and differentiate between superconductor types.

Contribution

It extends previous electrodynamic equations to include spin density and spin current dynamics, linking these to measurable superconductor properties and explaining differences between superconductor types.

Findings

Prediction of a spontaneous spin current near superconductor surfaces.

Quantitative relationships for expelled charge and interior electric fields.

Geometric interpretation of type I and II superconductor differences.

Abstract

In recent work we formulated a new set of electrodynamic equations for superconductors as an alternative to the conventional London equations, compatible with the prediction of the theory of hole superconductivity that superconductors expel negative charge from the interior towards the surface. Charge expulsion results in a macroscopically inhomogeneous charge distribution and an electric field in the interior, and because of this a spin current is expected to exist. Furthermore, we have recently shown that a dynamical explanation of the Meissner effect in superconductors leads to the prediction that a spontaneous spin current exists near the surface of superconductors. In this paper we extend the electrodynamic equations proposed earlier for the charge density and charge current to describe also the space and time dependence of the spin density and spin current. This allows us to determine the magnitude of the expelled negative charge and interior electric field as well as of the spin current in terms of other measurable properties of superconductors. We also provide a 'geometric' interpretation of the difference between type I and type II superconductors, discuss the relationship between our model and Slater's seminal work on superconductivity, and discuss the magnitude of the expected novel effects for elemental and other superconductors.