Reversible uniaxial strain tuning in atomically thin WSe2

Due to their unique band structure, single layers of transition metal dichalcogenides are promising for new atomic-scale physics and devices. It has been shown that the band structure and the excitonic transitions can be tuned by straining the material. Recently, the discovery of single-photon emission from localized excitons has put monolayer WSe₂ in the spotlight. The localized light emitters might be related to local strain potentials in the monolayer. Here, we measure strain-dependent energy shifts for the A, B, C, and D excitons for uniaxial tensile strain up to 1.4% in monolayer WSe₂ by performing absorption measurements. A gauge factor of -54\tfrac{{{meV}}}{ % }, -50\tfrac{{{meV}}}{ % }, +17\tfrac{{{meV}}}{ % }, and -22\tfrac{{{meV}}}{ % } is derived for the A, B, C, and D exciton, respectively. These values are in good agreement with ab initio GW-BSE calculations. Furthermore, we examine the spatial strain distribution in the WSe₂ monolayer at different applied strain levels. We find that the size of the monolayer is crucial for an efficient transfer of strain from the substrate to the monolayer.