Electronic correlations in the van der Waals ferromagnet Fe3GeTe2 revealed by its charge dynamics

The layered van der Waals ferromagnetic ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ harbors 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 ${T}_{C}\ensuremath{\sim}200$ 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 twofold 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, favoring the large anomalous Hall conductivity.