Revealing and controlling magnetism in WSe₂ via Se-vacancy states

In van der Waals-layered transition metal dichalcogenides, intrinsic defects such as transition metals and chalcogen vacancies are often observed. Transition metal vacancies generate magnetic properties; for example, the long-range magnetic order in PtSe₂ is induced by the Pt vacancies inherited from the formation of occupied mid-gap states. In contrast, the chalcogen vacancies generate unoccupied levels in the bandgap, which do not contribute to the total magnetic moment. In this talk, a gate-tunable magnetic order resonant with Se vacancy states in WSe₂ thin films by partially filling electrons will be presented. The Se-vacancy states were probed via photocurrent measurements with gating to convert unoccupied states to partially occupied states associated with photo-excited carrier recombination. The magneto-photoresistance hysteresis was modulated by gating, which is consistent with the density functional calculations. The two energy levels associated with Se vacancies split with increasing laser power, owing to the robust Coulomb interaction and strong spin-orbit coupling. Our results offer a new approach for controlling the magnetic properties of defects in optoelectronic and spintronic devices using van der Waals-layered semiconductors.