Shaping excitons distribution in 2D WSe2 via external strain field for positioned quantum emitters with stable magnetic response

Monolayer Transition-Metal Dichalcogenides (ML-TMDs) configure as suitable two-dimensional semiconductors, enlarging the family of graphene-like materials. ML-TMDs exhibit unique optical and electronic properties, such as strong spin-orbit coupling, inversion symmetry breaking, and valley-selective optical-selection rules. ML-TMDs can be easily fabricated via mechanical exfoliation and dry transfer techniques and can withstand up to 20% strain without breaking, being then feasible to exploit deformations to control their transport and optical properties. Furthermore, localized excitons in ML-TMDs provide single photons with high brightness[1]. Since both impurities and spatial strain gradients induce quantum emitters (QEs) in ML-TMDs [2], dynamic control over the strain field opens the possibility of engineering the QEs’ properties and exploiting their full potential for quantum technologies. Our piezoelectric device bursts into this context. It is a gold-covered PMN-PT piezoelectric micro-pillar array with a WSe2 monolayer dry-transferred on top. The QEs’ nucleation sites are arranged around the pillars, providing control of their position over a few microns[3] and allowing us to explore the QEs' response to external strain fields by deforming the piezoelectric substrate. We demonstrated that the QEs’ energy can be precisely tuned across a spectral range as large as tens of meV without changing the multi-photon emission probability[3]. We also observed that the external strain field reversibly modifies the QEs’ brightness. A strain-induced potential landscape is a possible explanation for this phenomenon, and we offered theoretical simulations based on this intuition exploiting an exciton diffusion model. We found good agreement between the theory and the experimental results, confirming that strain is a valuable tool even for brightening one specific emitter rather than another[4]. Since our piezoelectric actuator provides positioned single-photon sources with tunable energy and brightness, we wondered if the external strain field impacts the QEs' magnetic response. Measuring the g-factor of several single-photon lines as a function of the applied external stress, we found that despite changes in energy up to 10 meV, the variations in the g-factor always remain between the experimental error[5]. This result ensures the robustness of the QEs' spin degree of freedom, opening future possibilities in hybrid spintronic devices or photonic interfaces for quantum protocols.