Charge Density Wave State Suppresses Ferromagnetic Ordering in VSe2 Monolayers

Ferromagnetic ordering of monolayer vanadium dichalcogenides (VSe2 and VS2) has been predicted by density functional theory (DFT), and suggestive experimental evidence for magnetic ordering in VSe2 monolayers has been reported. However, such ferromagnetic ordering would be in stark contradiction to the known paramagnetic nature of the bulk VSe2. Herein, we investigate the electronic structure of VSe2 monolayers by angle-resolved photoemission spectroscopy (ARPES) and first-principles DFT. The ARPES measurements demonstrate the absence of spin-polarized bands for monolayers in close correspondence to nonmagnetic nature of the bulk VSe2. We demonstrate that the stabilization of the nonmagnetic state occurs due to the appearance of a charge density wave (CDW) state in VSe2 monolayers. In contrast to well-established 4 x 4 x 3 periodicity of the CDW in bulk VSe2, we identify a root 3 x root 7 unit cell for VSe2 monolayers from both scanning tunneling microscopy imaging and first-principles calculations. Moreover, DFT predicts that the root 3 x root 7 charge order state is energetically competitive with a ferromagnetic 1 x 1 state. This suggests that the experimentally observed CDW state is the nonmagnetic ground state of a perfect VSe2 monolayer, consistent with the absence of spin-polarized bands in ARPES measurements. Therefore, monolayer VSe2 is not an itinerant magnet.