The Ultrafast Quantum Dynamics group of Ermin Malic (Project B9) together with Rudolf Bratschitsch from the University of Münster revealed unexpected transport behavior of excitons in ultrathin semiconductors
Transport of charge carriers is at the heart of current nanoelectronics. In conventional materials, electronic transport can be conveniently controlled by applying external electric fields. However, the optoelectronic properties of the emerging material class of atomically thin semiconductors are governed by tightly bound excitons. These are neutral Coulomb-bound electron-hole pairs and as such their propagation cannot be controlled by electrical fields. Recently, strain engineering has been introduced to manipulate the propagation of excitons in these technologically promising materials. Strain-induced energy gradients give rise to exciton funneling up to a micrometer range. Excitons have been observed to propagate towards spatial regions with the strongest strain gradient, where the energy is minimal. However, the transport of dark excitons, which govern the optoelectronic response of these materials, has remained literally in the dark up till now.
In this joint theory-experiment work, the research groups of Ermin Malic and Rudolf Bratschitsch combined spatiotemporal photoluminescence measurements with microscopic many-particle theory to track the way of excitons in time, space and energy. They found that excitons surprisingly move away from high-strain regions. This anti-funneling behavior can be traced back to the dominating role of propagating dark excitons, which possess an opposite strain-induced energy variation compared to bright excitons. The findings open new possibilities to control the transport in materials dominated by excitons.
See also the press release by Philipps-University Marburg (in German).
R. Rosati, R. Schmidt, S. Brem, R. Perea-Causín, I. Niehues, J. Kern, J.A. Preuß, R. Schneider, S.M. de Vasconcellos, R. Bratschitsch, E. Malic
Dark exciton anti-funneling in atomically thin semiconductors
Nat. Commun. 12 (2021) 7221 DOI:10.1038/s41467-021-27425-y
Prof. Dr. Ermin Malic
SFB 1083 project B9
Tel.: 06421 28-22640