Isotropic Cooper Pairs with Emergent Sign Changes in Single-Layer Iron Superconductor

TL;DR

This paper models a single-layer iron superconductor, revealing emergent hole bands, hidden magnetic order, and isotropic Cooper pairs with sign changes, advancing understanding of pairing mechanisms in iron-based superconductors.

Contribution

It introduces a model showing emergent hole bands and sign-changing isotropic Cooper pairs in a heavily electron-doped FeSe monolayer, highlighting new pairing phenomena.

Findings

Emergent hole bands below Fermi level at the Brillouin zone center

Hidden magnetic order in the half metal state

Isotropic Cooper pairs with sign changes between bands

Abstract

We model a single layer of heavily electron-doped FeSe by spin-1/2 moments over a square lattice of iron atoms that include the 3d xz and 3d yz orbitals, at strong on-site Coulomb repulsion. Above half filling, we find emergent hole bands below the Fermi level at the center of the one-iron Brillouin zone in a half metal state characterized by hidden magnetic order and by electron-type Fermi surface pockets at wavenumbers that double the unit cell along the principal axes. "Replicas" of the emergent hole bands exist at lower energy in the two-iron Brillouin zone. Exact calculations with two mobile electrons find evidence for isotropic Cooper pairs that alternate in sign between the electron bands and the emergent hole bands.