Exciton propagation in atomically thin semiconductors
Department of Physics, University of Regensburg, Germany
Coulomb-bound electron-hole pairs, or excitons, have been in the focus of the solid-state research for many decades. They are of paramount importance for the fundamental understanding of interacting charge carriers in semiconductors. Recently, excitons in single layers of semiconducting transition-metal dichalcogenides (TMDCs) are found to combine a number of intriguing properties, including binding energies on the order of 0.5 eV, strong light-matter interaction and spin-valley coupling. It renders these electronic quasi-particles highly interesting both for fundamental research and future technology. In this context, it is important to consider that strongly-bound excitons in TMDCs are free to move in two dimensions. This has major implications, including the potential to deliberately manipulate exciton currents as well as to realize some of the more intriguing concepts using excitons at room temperature.
In this talk I will address the topic of exciton transport and discuss linear and nonlinear effective diffusion of excitons in semiconducting 2D materials. I will show how the interplay of many-particle interactions and propagation results in an apparent increase of diffusion coefficient by as much as two orders of magnitude, accompanied by characteristic changes in the exciton distribution profiles. I will further discuss the peculiar appearance of long-lived, micrometer-sized halo shapes in the exciton emission, indicating intricate collective phenomena and memory effects in the dynamics of Coulomb-bound quasiparticles in atomically thin materials. Overall, the obtained results should be both interesting from the perspective of fundamental exciton physics and highly relevant for the design of TMDC-based optoelectronic devices.
Alexey Chernikov received his Ph.D. at the University of Marburg (Germany) studying photo-excited electron dynamics and optics of III-V and IV-V semiconductors and their nanostructures. In 2013 he joined the group of Tony F. Heinz at Columbia University (New York, USA) with Alexander von Humboldt Fellowship grant as a postdoctoral researcher, working on excitonic phenomena in two-dimensional van der Waals materials and hybrid perovskites. Currently, he is leading a research group at the Regensburg University (Germany) focusing on fundamental studies and developing advanced concepts for precise manipulation of electronic many-body states in nanostructured materials.