Emergent Relativistic Effects in Condensed Matter
From Fundamental Aspects to Electronic Functionality
From Fundamental Aspects to Electronic Functionality
Nature Physics 14, 801–805 (2018)
Regensburg physicists around Dr. Tobias Korn, Institute for Experimental and Applied Physics of the University of Regensburg, have investigated atomically thin heterostructures of the two-dimensional materials molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) in an international collaboration with researchers from the TU Dresden and Columbia University in New York. They found out that the charge carriers (electrons and holes) in such a structure do not completely separate from each other, as previously thought, but are partly in both materials at the same time. This is an important finding, as well for basic research as for technological applications. The results were published in the journal "Nature Physics".
Monolayers of transition-metal dichalcogenides feature exceptional optical properties that are dominated by tightly bound electron–hole pairs, called excitons. Creating van der Waals heterostructures by deterministically stacking individual monolayers can tune various properties via the choice of materials and the relative orientation of the layers. In these structures, a new type of exciton emerges where the electron and hole are spatially separated into different layers. These interlayer excitons allow exploration of many-body quantum phenomena and are ideally suited for valleytronic applications. A basic model of a fully spatially separated electron and hole stemming from the K valleys of the monolayer Brillouin zones is usually applied to describe such excitons. Here, we combine photoluminescence spectroscopy and first-principles calculations to expand the concept of interlayer excitons. We identify a partially charge-separated electron–hole pair in MoS2/WSe2 heterostructures where the hole resides at the Γ point and the electron is located in a K valley. We control the emission energy of this new type of momentum-space indirect, yet strongly bound exciton by variation of the relative orientation of the layers. These findings represent a crucial step towards the understanding and control of excitonic effects in van der Waals heterostructures and devices.
SFB 1277
Doris Meier
Universität Regensburg
Phone: +49 (0) 941-943 2264
Email: SFB1277.Office@ur.de
