Direct Observation of Intrinsic Spin-Layer Coupling and Robust Valley Polarization in Bilayer MoS₂

Herein, direct evidence of intrinsic spin-layer coupling in bilayer MoS₂ through polarization-resolved photoluminescence measurements on fully suspended samples is presented. By eliminating substrate-induced symmetry breaking, such as electrostatic potential gradients and unintentional strain, the intrinsic valley dynamics of bilayer MoS₂ is isolated. The results reveal that the degree of circular polarization (DoCP) in bilayers remains significantly higher than that of monolayers across the entire temperature range. This observation cannot be explained by conventional thermal effects and instead indicates the presence of robust depolarization suppression mechanisms. In bilayer MoS₂, spin-layer coupling not only inhibits interlayer scattering by locking spin and valley indices to individual layers but also suppression spin-flip-mediated intervalley scattering by constraining the spin dynamics. Together, these effects maintain a high DoCP even under conditions that would normally induce strong depolarization via rapid intervalley and interlayer scattering pathways. The observation of enhanced DoCP in bilayers, despite larger excess energy typically enhances depolarization through intervalley scattering, indicates that the polarization is intrinsically linked to spin-layer coupling. These findings establish a bilayer MoS₂ as a compelling platform for exploring spin-valley-layer physics and advancing valleytronic applications.