Electronic correlations in the van der Waals ferromagnet Fe₃ GeTe₂ revealed by its charge dynamics

The layered van der Waals ferromagnetic $Fe_{3} GeTe_{2}$ harbors an unconventional interplay between topologyand magnetism, leading to a large anomalous Hall conductivity at low temperatures. Here, we investigate thetemperature dependence of its charge dynamics and reveal that upon entering the ferromagnetic state at $T_{C}∼200$ 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 twofold spectral weight transferindicates the important role of the Hund’s coupling as primary source for electronic correlations and signals anincoherent-coherent crossover at low temperatures. Our findings also convey the electronic environment, basedon nodal-line topological states, favoring the large anomalous Hall conductivity.