Spin currents, relativistic effects and the Darwin interaction in the theory of hole superconductivity

TL;DR

This paper predicts macroscopic spin currents in superconductors and demonstrates that relativistic effects and the Darwin interaction are crucial for understanding and stabilizing the superconducting state.

Contribution

It introduces the role of the Darwin interaction and relativistic electron speeds in the theory of hole superconductivity, highlighting their importance in ground state properties.

Findings

Darwin interaction is attractive for spin currents

Electrons move at relativistic speeds in superconductors

Spin currents imply Darwin interaction stabilizes superconductivity

Abstract

The existence of macroscopic spin currents in the ground state of superconductors is predicted within the theory of hole superconductivity. Here it is shown that the electromagnetic Darwin interaction is attractive for spin currents and repulsive for charge currents. It is also shown that the mere existence of spin currents implies that some electrons are moving at relativistic speeds in macroscopic superconductors, which in turn implies that the Darwin interaction plays a fundamental role in stabilizing the superconducting state.