Dirac fermions in Fe ultra-thin film

TL;DR

This paper demonstrates the existence of massive Dirac fermions in ultrathin Fe films with perpendicular magnetization, revealing topological properties and quantized Hall conductivity arising from band inversion and spin-orbit coupling.

Contribution

It identifies and characterizes massive Dirac fermions in Fe ultrathin films, linking their presence to band inversion and spin-orbit effects, and explores their topological and magnetic implications.

Findings

Four massive Dirac fermions near the Fermi level due to band inversion.

Quantized Hall conductivity of 2e^2/h when the chemical potential is in the Dirac gap.

Finite Chern number (+2) indicating nontrivial topological properties.

Abstract

We show the existence of massive Dirac fermions in electronic band structures of a few Fe atomic layers with perpendicular magnetization. Based on a tight binding model fitted to ab-initio band structure, we observe four distinct massive Dirac fermions near the Fermi level, which result from atomic spin-orbit coupling of Fe and a band inversion between Fe $4s$-$3d_{x^2-y^2}$ hybrid orbital band and $3d_{xy}$ orbital band. These lead to a valence band with finite Chern integer (+2) and chiral edge modes near the Fermi level. When the chemical potential is set inside the Dirac gap by carrier doping, the Hall conductivity exhibits a plateau-like structure with quantized value $2\frac{e^2}{h}$, and orbital magnetization shows a prominent increase, latter of which is mostly due to chiral orbital motion of electrons along the edge modes. We discuss the stability of the Dirac fermions in Fe(001) monolayer on MgO(001) substrate and Fe(001) bilayer case.