Optical excitations in transition metal dichalcogenide heterostructures under pressure

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The main goal of the project is to gain a comprehensive understanding of interlayer coupling in transition metal dichalcogenide heterostructures. In many cases, interlayer interactions lead to emergent electronic and optical properties that are fundamentally distinct from those of the constituent layers. A critical parameter is the interlayer coupling strength with its moiré pattern. It is given by the choice of the materials and the fabrication process, and is typically considered as an unchangeable property of the system. Applied hydrostatic or uniaxial pressure, however, strongly affects the interlayer distance and thus the electronic coupling. Therefore, one can tune the interlayer excitons and moiré bands by pressure. In our joint experiment-theory effort, we will fabricate heterostructures of transition metal dichalcogenides and investigate their (transient) optical properties depending on pressure. Experimental techniques comprise (ultrafast) photoluminescence, absorption and second harmonic generation spectroscopy. As a theoretical approach, we will use a combination of ab-initio many-body investigations and model development to tackle the size of the investigated system. Furthermore, we will engineer compressive strain landscapes, which will allow for funneling of interlayer excitons and eventually the investigation of collective phenomena such as Bose-Einstein condensation.