Selective Spin-Triplet and Spin-Singlet Interlayer Exciton Emission in WS₂/WSe₂ Heterostructure for All-Optical Valley Switch

Spin-splitting in transition metal dichalcogenides (TMDs) heterostructure generate spin-singlet and spin-triplet interlayer exciton (IX) with unique spin-valley physics. Although selective singlet and triplet IX emission can be achieved by applying electric and magnetic field, the device structure is complex and low-temperature condition is demanding. Here, by selectively coupling singlet or triplet IX dipole of WS₂/WSe₂ heterostructure to a SiO₂ sphere cavity, we can actively control the emissive IX species at room temperature in an all-optical route. We find the triplet IX dipole is almost along the out-of-plane orientation, whereas, only 69% of the singlet IX dipole is out-of-plane. Consequently, triplet IX emission is enhanced more greatly in TMDs/SiO₂ cavity hybrid structure due to that out-of-plane dipole presents higher Purcell factor for SiO₂ cavity. By utilizing the selective enhancement of singlet and triplet IX emission, we demonstrated an all-optical valley switch. Our finding provides a convenient approach to control the fine structure of IX and develop their applications in valleytronics.