Hole core in superconductors and the origin of the Spin Meissner effect

TL;DR

This paper proposes a hidden 'hole core' within superconductors that explains the Spin Meissner effect and charge expulsion, linking microscopic electronic states to macroscopic superconducting phenomena.

Contribution

It introduces the concept of a hole core at the Fermi surface that becomes singly occupied in the superconducting state, providing a new microscopic explanation for the Spin Meissner effect.

Findings

Hole core radius is half the London penetration depth.

Expulsion of negative charge occurs within a London penetration depth.

Development of a spin current during the transition to superconductivity.

Abstract

It is proposed that superconductors possess a hidden `hole core' buried deep in the Fermi sea. The proposed hole core is a small region of the Brillouin zone (usually at the center of the zone) where the lowest energy states in the normal state reside. We propose that in the superconducting state these energy states become {\it singly occupied} with electrons of a definite spin helicity. In other words, that holes of a definite spin helicity condense from the top to the bottom of the band in the transition to superconductivity, and electrons of that spin helicity `float' on top of the hole core, thus becoming highly mobile. The hole core has radius $q_0=1/2\lambda_L$, with $\lambda_L$ the London penetration depth, and the electrons expelled from the hole core give an excess negative charge density within a London penetration depth of the real space surface of the superconductor. The hole core explains the development of a spin current in the transition to superconductivity (Spin Meissner effect) and the associated negative charge expulsion from the interior of metals in the transition to superconductivity, effects we have proposed in earlier work to exist in all superconductors and to be at the root of the Meissner effect.