Ultrafast dynamics in atomically thin transition metal dichalcogenides in a magnetic field

• Applicants: Professor Dr. Rudolf Bratschitsch; Professor Dr. Andreas Knorr
• Subject Area: Experimental Condensed Matter Physics ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Theoretical Condensed Matter Physics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 420760124

Atomically thin semiconducting transition metal dichalcogenides (TMDs) unite nearly ideal two-dimensional confinement of charge carriers and strongly reduced dielectric screening from the environment. The combination of both results in strong attractive Coulomb interactions between electron-hole pairs which form a variety of bright and dark excitons as well as tightly bound charged excitons (trions) and bound two-exciton states (biexcitons). These fundamental excitations play a dominant role in the optical properties of atomically thin TMDs and provide ideal prerequisites to investigate new exciton physics in two dimensions. In particular, the ultrafast nonlinear optical response of atomically thin TMDs is governed by many-body exciton-exciton, exciton-electron, and exciton-phonon interactions. Consequently, the manipulation of many-body interactions by external magnetic fields, modifying excitonic excitation channels and their dynamics, is of particular interest for an in-depth understanding of underlying microscopic processes, which determine the optical response, and for future applications of atomically thin TMDs. The main goal of the proposed project is to elucidate in a joint theory and experiment effort the ultrafast dynamics and relaxation mechanisms between magnetic-field-controlled intra- and intervalley TMD excitons, trions, and biexcitons in atomically thin (TMDs). Experimentally, we will measure the dynamics in time-resolved photoluminescence and pump-probe experiments in different magnetic field geometries and with controlled doping. In the theory part, we plan to extend our microscopic formalism of pump-probe spectroscopy to include incoherent, in time evolving effects such as relaxation and dephasing, and dark exciton formation, dominating in experiments at finite delay time. These processes occur simultaneously in the temporal dynamics of momentum- and spin-bright as well as momentum- and spin-dark excitons. The gained insights into the fundamental many-particle processes governing the ultrafast dynamics in these atomically thin two-dimensional nanostructures will be of crucial importance for designing and engineering novel TMD-based optoelectronic devices.

• DFG Programme: Research Grants