An international research team led by the University of Göttingen has, for the first time, observed the accumulation of a physical phenomenon that plays a role in the conversion of sunlight into electrical energy in 2D materials. Scientists have succeeded in making quasiparticles – known as Dark Moiré interlayer excitons – visible and explaining their formation using quantum mechanics. Researchers show how a newly developed experimental technique in Göttingen. provides deep insights at the microscopic level, which will be relevant for the development of future systems. The results were published in Mother nature.
Atomically thin structures made of two-dimensional semiconductor materials are promising candidates for future electronics components. Interestingly, the properties of these semiconductors can be controlled in unusual ways: like Lego bricks, the atomically thin layers can be stacked on top of each other. However, there is another important trick: while Lego bricks can only be stacked on top – either straight or twisted at an angle of 90 degrees – the angle of rotation in the semiconductor structure can be changed. It is precisely this angle of rotation that is of interest for the generation of new types of solar cells.
However, while changing this angle can reveal breakthroughs for new technologies, it also leads to experimental challenges. In fact, typical experimental approaches only have oblique access to moiré interlayer excitons, therefore these excitons are commonly referred to as “dark” excitons. we have actually managed to make these dark excitons visible,” says Dr. Marcel Reutzel, Junior Research Group Leader at the Faculty of Physics at the University of Göttingen. “This allows us to measure how excitons form on a timescale of a millionth of a millionth of a millisecond. We can describe the dynamics of the formation of these excitons using the theory of quantum mechanics developed by the research group of Professor Ermin Malic in Marburg. ”
“These results not only give us fundamental insight into the formation of dark moiré interlayer excitons, but also open up a whole new viewpoint to allow scientists to study the optoelectronic properties of fascinating new materials”, says Professor Stefan Mathias, Director of Studies at the Faculty of Physics at the University of Göttingen. “This experiment is revolutionary because, for the first time, we have detected the signature of the Moiré potential imprinted on the exciton, ie the impact of the combined properties of the two twisted semiconductor layers. In the future, we will study this specific effect in more detail to learn more about the properties of the resulting materials.”
This research has been made possible thanks to to the German Research Foundation (DFG) which funded the CRC “Handle of Energy Conversion on Atomic Scales” and “Mathematics of Experiment” in Göttingen, and the CRC “Structure and Dynamics of Inner Interfaces” in Marburg.