Why holes are not like electrons. IV. Hole undressing and spin current in the superconducting state

TL;DR

This paper proposes a novel theory of superconductivity driven by spin-split hole states and spin currents, emphasizing the role of Coulomb exchange interactions and spin chirality in the superconducting state.

Contribution

It introduces a new scenario where spin splitting and hole undressing lead to superconductivity, supported by Coulomb exchange favoring spin-chiral states.

Findings

Spin splitting reduces Coulomb repulsion in superconductors.

Superconductors have a spin-split hole core and Fermi surface.

The theory explains the Spin Meissner effect and negative charge expulsion.

Abstract

In paper III of this series (arXiv:0901.3612) we proposed a scenario of superconductivity driven by hole "undressing" that involved a complete redistribution of the occupation of single particle energy levels: the holes near the top of the band were proposed to all condense to the bottom of the band. Here we consider a less drastic redistribution involving electrons with a definite spin chirality and show that it is in fact energetically favored by the Coulomb exchange matrix element $J$ over the scenario proposed earlier. It is shown that spin splitting with chiral states reduces the Coulomb repulsion and hence that the Coulomb repulsion promotes spin splitting. Superconductors are proposed to possess a spin-split hole `core' at the bottom of the electronic conduction band in addition to a spin-split Fermi surface. The new scenario leads naturally to the existence of a spin current in the superconducting state and is consistent with the Spin Meissner effect and negative charge expulsion discussed earlier within the theory of hole superconductivity.