Spin Hall effect in iron-based superconductors: A Dirac-point effect

TL;DR

This paper theoretically investigates the intrinsic spin Hall effect in iron-based superconductors, revealing that Dirac cones below the Fermi energy significantly enhance SHE, especially in heavily hole-doped regimes like KFe₂As₂.

Contribution

It demonstrates that Dirac-point effects can induce large SHE in iron-based superconductors, even with modest spin-orbit coupling, highlighting a new mechanism for spin transport.

Findings

Large SHE predicted in heavily hole-doped regimes

Spin Hall conductivity comparable to platinum

Dirac cone contributions dominate SHE enhancement

Abstract

We have theoretically explored the intrinsic spin Hall effect (SHE) in the iron-based superconductor family with a variety of materials. The study is motivated by an observation that, in addition to an appreciable spin-orbit coupling in the Fe 3d states, a character of the band structure in which Dirac cones appear below the Fermi energy may play a crucial role in producing a large SHE. Our investigation does indeed predict a substantially large spin Hall conductivity in the heavily hole-doped regime such as KFe$_2$As$_2$. The magnitude of the SHE has turned out to be comparable with that for Pt despite a relatively small spin-orbit coupling, which we identify to come from a huge contribution from the gap opening induced by the spin-orbit coupling at the Dirac point, which can become close to the Fermi energy for the heavy hole doping.