Magnetic Proximity Engineering of Valley Pseudospins in a Twisted WSe2 Moiré Superlattices.

Moiré excitons in twisted transition metal dichalcogenides form a highly tunable and strong correlated system with controllable valley pseudospins offering a promising quantum platform for valleytronics. However, due to inherent magnetic moment, their valley characteristics are fixed and exhibit weak response to external perturbations, limiting their application in spintronics and valleytronics. Here, we manipulate the valley polarization and valley splitting of moiré exciton utilizing magnetic proximity effect through constructing van der Waals heterostructure consisting of twisted WSe2 homobilayers and ferromagnetic 1T-VSe2. Photoluminescence measurements reveal that interfacial coupling deepens the moiré potential by ∼18% (from 45.33 to 53.57 meV). Furthermore, the magnetic proximity effect breaks the time-reversal symmetry in twisted WSe2, producing a zero-field valley splitting of ∼0.9 meV, corresponding to an effective magnetic field of ∼1.71 T. This coupling increases the Landé g-factor of moiré excitons and enhances the magnetic-filed response of their valley polarization by approximately 200% and 300%, respectively. Temperature-dependent measurements further reveal that the thermal evolution of valley polarization is governed by the spin thermodynamics of the ferromagnetic layer, marked by its sharp decrease with rising temperature. These findings establish the magnetic proximity modulation as a powerful and deterministic strategies to control valley pseudospins on a moiré exciton, paving the way for the development of valleytronics and quantum spin devices.