Origins of the anomalous Hall conductivity in the symmetry enforced Fe3GeTe2 nodal-line ferromagnet

TL;DR

This study clarifies the origins of anomalous Hall conductivity in Fe3GeTe2, showing it arises from multiple symmetry-protected features and can be enhanced by electron doping, challenging previous assumptions about nodal lines.

Contribution

The paper identifies the true sources of AHC in Fe3GeTe2, emphasizing the roles of mirror-symmetry-protected nodal lines, Weyl points, and SOC-induced gaps, providing new insights into its electronic structure.

Findings

Nodal lines are symmetry-protected and do not directly cause AHC.

Weyl points contribute significantly to AHC within certain energy ranges.

Electron doping can potentially quadruple the AHC.

Abstract

Fe$_3$GeTe$_2$ has gained attention in the condensed matter community for its potential to be exfoliated into thin films with ferromagnetic (FM) order, thanks to its van der Waals layered structure and significant intrinsic anomalous Hall conductivity (AHC). In this work, we analyze the electronic structure and show that, contrary to prior claims, the bulk of the AHC cannot arise from gapped nodal lines. By studying the material's symmetry properties, both with and without spin-orbit coupling (SOC) and across paramagnetic and FM phases, we find that Fe$_3$GeTe$_2$ hosts mirror-symmetry-protected nodal lines, which support surface drumhead states. Additionally, we identify three key sources of AHC: nodal lines in the paramagnetic phase gapped by the FM order, Weyl points within specific energy ranges, and gaps between spin-up and spin-down bands caused by SOC. Finally, our calculations suggest that electron doping could increase the AHC up to four times compared to its value at the computed Fermi level.