Extended valley lifetime and giant energy splitting induced by chiral plasmon-valley exciton selective coupling

The broken inversion symmetry in monolayer transition metal dichalcogenides (TMDs) permits light of specific helicities to address valley-polarized excitonic states, which could serve as inherent information carriers. Achieving large valley energy splitting and long valley lifetimes at room temperature is essential for practical valleytronic applications, yet remains challenging due to strong intervalley interactions. To tackle this, we coupled a single chiral plasmonic nano-resonator with monolayer MoS₂ to prolong the latter's valley polarization through chiral plasmon-valley exciton selective coupling. Our findings show that the selective coupling significantly prolongs the valley exciton population contrast lifetime in the coupled MoS₂, originating from valley energy splitting induced by the selective coupling that breaks the energy degeneracy between the valleys. The experimental results are further corroborated by an effective model, revealing distinct coupling strengths for the K and $K^{\text{'}}$ valleys and a strong relation between plasmon-exciton energy detuning and valley polarization. This work offers new possibilities for information encoding and storage by exploiting the valley degree of freedom in cavity-coupled low-dimensional semiconductors.