Effect of Coulomb Interactions on the Electronic and Magnetic Properties of Two-Dimensional CrSiTe3 and CrGeTe3 Materials

We investigate the electronic and magnetic structures of two-dimensional transition metal tri-chalcogenide CrSiTe3 and CrGeTe3 materials by carrying out first-principles calculations. The single-layer CrSiTe3 and CrGeTe3 are found to be a ferromagnetic insulator, where the presence of the strong dp sigma-hybridization of Cr e(g)-Te p plays a crucial role for the ferromagnetic coupling between Cr ions. We observe that the bandgaps and the interlayer magnetic order vary notably depending on the magnitude of on-site Coulomb interaction U for Cr d electrons. The bandgaps are formed between the Cr e(g) conduction bands and the Te p valence bands for both CrSiTe3 and CrGeTe3 in the majority-spin channel. The dominant Te p antibonding character in the valence bands just below the Fermi level is related to the decrease of the bandgap for the increase of U. We elucidate the energy band diagram, which may serve to understand the electronic and magnetic properties of the ABX(3)-type transition metal tri-chalcogenides in general.