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

## TL;DR

This study shows that bilayer MoS2 has strong and stable circular polarization due to intrinsic spin-layer coupling, making it a promising material for valleytronic applications.

## Contribution

The paper provides direct experimental evidence of intrinsic spin–layer coupling in bilayer MoS2, revealing its role in suppressing depolarization.

## Key findings

- Bilayer MoS2 shows higher circular polarization than monolayers across all temperatures.
- Spin–layer coupling suppresses interlayer and intervalley scattering, maintaining polarization.
- Substrate-free measurements confirm the intrinsic nature of the observed effects.

## Abstract

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.

This study experimentally demonstrates finite and even enhanced circular polarization in bilayer MoS2, despite its centrosymmetric 2H stacking, across all temperatures. The degree of circular polarization exceeds that of monolayers, attributed to spin–layer coupling and suppression of spin‐flip processes. Substrate‐free measurements confirm intrinsic origins, offering new insights into spin and valley control in 2D semiconductors.© 2025 WILEY‐VCH GmbH