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Submitted – in-review process

  • W. Bennecke, T. L. Dinh, J.P. Bange, D. Schmitt, M. Merboldt, L. Weinhagen, B. van W., F. Frassetto, L. Poletto, M. Reutzel, D. Steil, D.R. Luke, S. Mathias, GS Jansen, arXiv:2502.18269 (2025).

    Two-dimensional transition metal dichalcogenides (TMDs) and organic semiconductors (OSCs) have emerged as promising material platforms for next-generation optoelectronic devices. The combination of both is predicted to yield emergent properties while retaining the advantages of their individual components. In OSCs the optoelectronic response is typically dominated by localized Frenkel-type excitons, whereas TMDs host delocalized Wannier-type excitons. However, much less is known about the spatial and electronic characteristics of excitons at hybrid TMD/OSC interfaces, which ultimately determine the possible energy and charge transfer mechanisms across the 2D-organic interface. Here, we use ultrafast momentum microscopy and many-body perturbation theory to elucidate a hybrid exciton at an TMD/OSC interface that forms via the ultrafast resonant Förster energy transfer process. We show that this hybrid exciton has both Frenkel- and Wannier-type contributions: Concomitant intra- and interlayer electron-hole transitions within the OSC layer and across the TMD/OSC interface, respectively, give rise to an exciton wavefunction with mixed Frenkel-Wannier character. By combining theory and experiment, our work provides previously inaccessible insights into the nature of hybrid excitons at TMD/OSC interfaces. It thus paves the way to a fundamental understanding of charge and energy transfer processes across 2D-organic heterostructures.

    https://arxiv.org/abs/2502.18269, https://arxiv.org/abs/2411.14993

  • P. Werner, W. Bennecke, J. P. Bange, G. Meneghini, D. Schmitt, M. Merboldt, A. M. Seiler, A. A. AlMutairi, K. Watanabe, T. Taniguchi, G. S. M. Jansen, J. Liu, D. Steil, S. Hofmann, R. T. Weitz, E. Malic, S. Mathias, M. Reutzel, The role of non-equilibrium populations in dark exciton formation

    In two-dimensional transition metal dichalcogenide structures, the optical excitation of a bright exciton may be followed by the formation of a plethora of lower energy dark states. In these formation and relaxation processes between different exciton species, non-equilibrium exciton and phonon populations play a dominant role, but remain so far largely unexplored as most states are inaccessible by regular spectroscopies. Here, on the example of homobilayer 2H-MoS , we realize direct access to the full exciton relaxation cascade from experiment and theory. By measuring the energy- and in-plane momentum-resolved photoemission spectral function, we reveal a distinct fingerprint for dark excitons in a non-equilibrium excitonic occupation distribution. In excellent agreement with microscopic many-particle calculations, we quantify the timescales for the formation of a non-equilibrium dark excitonic occupation and its subsequent thermalization to 85~fs and 150~fs, respectively. Our results provide a previously inaccessible view of the complete exciton relaxation cascade, which is of paramount importance for the future characterization of non-equilibrium excitonic phases and the efficient design of optoelectronic devices based on two-dimensional materials.

    https://arxiv.org/abs/2505.06074v1