Measurement of electronic structure in van der Waals ferromagnet Fe_5-x GeTe₂

As a van der Waals ferromagnet with high Curie temperature, Fe5-x GeTe2 has attracted tremendous interests recently. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES), we systematically investigated the electronic structure of Fe5-x GeTe2 crystals and its temperature evolution. Our ARPES measurement reveals two types of band structures from two different terminations with slight k(z) evolution. Interestingly, across the ferromagnetic transition, we observed the merging of two split bands above the Curie temperature, suggesting the band splitting due to the exchange interaction within the itinerant Stoner model. Our results provide important insights into the electronic and magnetic properties of Fe5-x GeTe2 and the understanding of magnetism in a two-dimensional ferromagnetic system.