Coulomb-interaction effect on the two-dimensional electronic structure of the van der Waals ferromagnet Cr2Ge2Te6

In order to investigate the electronic properties of the semiconducting van der Waals ferromagnet Cr2Ge2Te6 (CGT), where ferromagnetic layers are bonded through van der Waals forces, we have performed angle-resolved photoemission spectroscopy measurements and density-functional theory (DFT + U) calculations. The valence-band maximum at the Gamma point is located similar to 0.2 eV below the Fermi level, consistent with the semiconducting property of CGT. Comparison of the experimental density of states with the DFT calculation has suggested that Coulomb interaction between the Cr 3d electrons U-eff similar to 1.1 eV. The DFT + U calculation indicates that magnetic coupling between Cr atoms within the layer is ferromagnetic if Coulomb U-eff is smaller than 3.0 eV and that the interlayer coupling is ferromagnetic below U-eff similar to 1.0 eV. We therefore conclude that, for U-eff deduced by the experiment, the intralayer Cr-Cr coupling is ferromagnetic and the interlayer coupling is near the boundary between ferromagnetic and antiferromagnetic, which means experimentally deduced U-eff is consistent with the theoretical ferromagnetic condition.