Optical helicity control of magnetic dynamics in TMD/2D Magnet heterostructure*

2D van der Waals magnets provide versatile opportunities for controlling magnetization switching and studying the dynamics. With 2D magnet in proximity with a transition metal chalcogenide (TMD), many novel phenomena will happen such as magnetic proximity effect, valley Zeeman splitting and valley polarization in TMDs. On the other hand, when the 2D magnet comes down to few-layer limit, its magnetization will be more easily influenced by spin transferred from TMD. Here, we investigate spin and magnetization dynamics in TMD/2D magnet heterostructures, specifically WS₂/2L-Fe₃GeTe₂ (FGT)/Bi₂Te₃ heterostructure, using an ultrafast optical pump-probe technique. Different wavelengths are used to pump resonantly in TMD layer and probe magnetization in 2D magnet layer separately.  By performing photoluminescence (PL) measurements prior to time-resolved measurements, we observed much reduced PL intensity in monolayer WS₂ when interfaced with FGT, indicating strong charge transfer. The strong charge transfer and spin-valley locking nature in TMDs provides an opportunity to inject specific spin from WS₂ into FGT and modulate magnetic properties of the FGT by pumping with different optical helicity. We successfully observed difference in ultrafast magnetization dynamics with left and right circular polarized pump, which indicates possibly the combination of a thermal demagnetization effect and a much faster spin injection process. Time-resolved measurements and control experiments are still ongoing to be able to better analyze and explain the observed dynamics. We also perform measurements on heterostructures of TMD/magnetic semiconductors.