Oral: Ultrafast spin dynamics in Vanadium-doped Tungsten diselenide monolayer

The substitution of transition metal atoms with magnetic atoms in transition metal dichalcogenides (TMDs), such as vanadium (V), introduces and enables the manipulation of magnetism in these ultrathin materials. V-doped tungsten diselenide (V-WSe₂) exhibits ferromagnetic order at room temperature. However, studies on the ultrafast spin dynamics of these materials, especially at the microscopic scale where dopant levels vary, remain limited. V dopants introduce localized states within the WSe₂ bandgap, shifting the Fermi level into the valence band and resulting in p-type semiconducting behavior. Consequently, positive trions dominate in regions with high doping levels. By utilizing confocal microscopy, we can map the spatial distribution of trions and excitons through photoluminescence, allowing us to determine the V-doping level at the micrometer scale. Subsequently, we employ ultrafast time-resolved magneto-optical Kerr effect (TR-MOKE) microscopy to investigate spin dynamics in V-WSe₂ at high trion or exciton distributions. Our observations reveal that the spin lifetime of trions is significantly longer than that of excitons. This finding is consistent with previous reports of room-temperature ferromagnetism in V-WSe₂. These results provide valuable insights into the ultrafast spin dynamics of magnetic atom-doped ultrathin semiconductors and the potential for controlling spin in 2D materials by light.