Electronic correlations in the van der Waals ferromagnet Fe$_3$GeTe$_2$ revealed by its charge dynamics

TL;DR

This study explores how electronic correlations and topological states in Fe$_3$GeTe$_2$ influence its charge dynamics and anomalous Hall effect, revealing a temperature-driven spectral weight transfer and incoherent-coherent crossover.

Contribution

It uncovers the role of Hund's coupling in electronic correlations and demonstrates the impact of topological states on the material's Hall conductivity.

Findings

Spectral weight shifts from mid-infrared to far- and near-infrared frequencies below T_C.

Identification of an incoherent-coherent crossover at low temperatures.

Electronic environment favors large anomalous Hall conductivity due to nodal-line topological states.

Abstract

The layered van der Waals ferromagnetic Fe$_3$GeTe$_2$ harbours an unconventional interplay between topology and magnetism, leading to a large anomalous Hall conductivity at low temperatures. Here, we investigate the temperature dependence of its charge dynamics and reveal that upon entering the ferromagnetic state at $T_C \sim 200$ K and further lowering the temperature there is the onset of a gradual spectral weight reshuffling from the mid-infrared range towards far- as well as near-infrared frequencies. This two-fold spectral weight transfer indicates the important role of the Hund's coupling as primary source for electronic correlations and signals an incoherent-coherent crossover at low temperatures. Our findings also convey the electronic environment, based on nodal-line topological states, favouring the large anomalous Hall conductivity.