Excited state charge dynamics and optical response of 2D materials: interplay excitons and phonons

Talat S. Rahman
Department of Physics, University of Central Florida, Orlando, Florida

DIPC seminar room

29 February, 26 March 2024
11h00 – 13h00

A striking feature of 2D transition metal dichalcogenides (TMDs) is the large exciton binding energy, which together with strong interactions between the electrons, holes, excitons, and phonons, promise the potential for applications in energy harvesting. These strong nonlinearities may be reflected in the characteristics of the resulting photocurrent and the emission spectra, for example, through high harmonic generation. In this talk after attributing the experimentally observed anomalous optical band gap energy redshift, with increasing isotope mass, in single layer MoS2, to strong exciton-phonon coupling, we will turn to phonon-assisted charge and exciton dynamics and photoluminescence in single layer and bilayer MoS2 and WSe2 [1,2]. I will show, through application of time dependent density functional theory (TDDFT) and many-body theory, that the (momentum-resolved) intra- and inter-valley dynamics, and photoluminescence in these 2D TMDs is a result of complex collective response involving the free charges, bright and dark excitons, and phonons. Our conclusions are validated by experimental data where available.

1. N. Ud Din, V. Turkowski and T. S Rahman, 2D Materials 8, 025018 (2021)
2. J. Shi, V. Turkowski, and T. S. Rahman, Phys. Rev B 107, 155431 (2023).

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