Strain fingerprinting of exciton valley character in 2D semiconductors

Momentum-indirect intervalley excitons define optoelectronic properties of 2D semiconductors but are challenging to detect due to their weak coupling to light. Complexities associated with momentum-selective probes further limit the identification of exciton's valley content. Here, we show that under mechanical strain, the excitons exhibit valley-specific energy shifts, allowing their valley fingerprinting. To this end, we apply controlled strain up to 2% at cryogenic temperatures in suspended 2D materials. This approach allows us to identify multiple previously inaccessible excitons with wavefunctions localized in K, Γ, and Q valleys, as well as different types of localized excitons. Moreover, we demonstrate up to 80 meV energy tuning of single photon emitters associated with localized states. Overall, our simple optomechanical approach may be used to tune and unravel intervalley excitons in various 2D systems.