Understanding enhanced valley polarization in stacked MoS₂ bilayers with zero twist angle

Improving the degree of valley polarization (DVP) in transition metal dichalcogenides (TMDs) is crucial for exploiting the valley degree of freedom in valleytronic applications. While extensive efforts have focused on enhancing DVP in TMD monolayers, investigations of this property in bilayer and multilayer systems remain limited. Here, MoS₂ bilayers were fabricated by stacking two monolayers in a parallel alignment (0° twist angle), and a pronounced enhancement in DVP was observed compared with that of MoS₂ monolayers. Temperature-dependent spectroscopy demonstrates that this enhancement arises from two cooperative mechanisms: preferential phonon-assisted carrier relaxation into the Λ valley, which suppresses intervalley scattering, and reduced electron-hole exchange in interlayer excitons, which lowers valley depolarization. These results identify stacking-controlled interlayer hybridization as a powerful route to engineer valley dynamics in layered semiconductors.