Control of light-matter interaction in 2D transition metal dichalcogenides via strain engineering

• Applicant: Dr. Florian Dirnberger
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 451072703

Following the observation of bright luminescence in single layers of transition metal dichalcogenides (TMDs), the past decade has witnessed the emergence of exceptional physics in this new class of optically active materials. Reports about room temperature excitonics, highly stable single photon emission and numerous valley-related anomalies keep attracting enormous scientific interest in these new two-dimensional materials. In this regard, the realization that the unique valley structure entails coherence properties, which result in a (partially) linearly polarized emission at cryogenic temperatures, beyond doubt reflects a truly outstanding example of the remarkable physics encountered in TMDs. This phenomenon, termed Valley Coherence, has triggered profound excitement in the research community, not the least due to its potential for applications in quantum computation. Harnessing these promising developments for technological applications now demands sufficient external control over the key interactions between light and matter. Amidst the different approaches, engineering strain in the two-dimensional lattices is currently emerging as a very powerful tool. Here, TMDs offer an unrivaled advantage over the more rigid, classical semiconductors: They have been reported to withstand extreme deformations of the lattice unit cell, up to 10%, before the deformations become inelastic and the material is permanently damaged.Utilizing this exceptional mechanical property to control various light-matter interactions in TMDs via strain engineering is the goal of this project. At the beginning, different experimental platforms for the implementation of nanoscale strain in TMDs, such as nanostructured substrates, or the controlled indention by an AFM tip will be explored. While the impact of strain on the optical properties of the system will be monitored and characterized through standard optical spectroscopy, different microscopy techniques capable of imaging the morphology of single layers can be applied to quantify the extent of strained regions. Complementing the results of the optical spectroscopy, this insight will serve as a basis for the development of theoretical models to estimate the effects of strain on the excitonic states and the band structure. Having established an experimental platform for nanoscale strain, the project will focus on the interplay between strain, exciton funneling and the formation of quantum emitters and the impact of strain on Valley Coherence properties.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professor Vinod M. Minon