Synergistic Control of Valley Polarization and Raman Enhancement via Chiral Plexcitons in WS ₂ /J‐Aggregates Heterostructures

Abstract Active manipulation of light–matter interaction at the nanoscale, especially in the strong coupling regime, is critical for advanced biochemical and optical applications. However, simultaneous control over multiple degrees of freedom such as spin‐valley and chirality, remains challenging because the weak bonding among them. Here, a compact Au@Ag nanorod/ J‐aggregates/WS 2 heterocavity is proposed, which enables not only valley polarization manipulation but also tunable Raman enhancement at room temperature. Two species of excitons, from both the K/K' valleys in the WS 2 monolayer and the chiral J‐aggregates, are coupled with a single nanocavity mode exhibiting pronounced double Rabi splittings (142 and 130 meV). Utilizing the plasmon–biexciton strong coupling effect, a degree of circular polarization (DCP) reaching up to 46% is achieved, which is among the largest values reported for room‐temperature operation. And detuning‐dependent Raman enhancements ranging from 10 4 to 10 7 has also been observed. Theoretical research reveals that mirror‐symmetry breaking induced by the chiral J‐aggregates and inclined Au@Ag nanocavity lifts the degeneracy between σ + and σ − plexciton modes, which causes the pronounced valley‐selective emission. Meanwhile, valley‐polarized excitons can subsequently reshapes the near‐field distribution, yielding tunable Raman enhancement from the same nanocavity. These results open rich possibilities toward multifunctional plasmon‐enhanced spectroscopy, chiral light–matter interfaces, and integrated nanophotonic devices.