Capturing exciton wavefunctions by time-resolved photoemission orbital tomography

PC Special Seminar
Datum: 06.06.2025
Uhrzeit: 10:30
Vortragende(r): Wiebke Bennecke
Georg-August-Universität Göttingen
Ort: Building G
Raum: 2.06
Gastgeber: Ralph Ernstorfer

Excitons are realizations of a correlated many-body wavefunction, consisting of a Coulomb-bound electron-hole pair. They are the dominant excitations in organic and two-dimensional semiconductors. Thus, to exploit the full optoelectronic potential of these materials, a complete microscopic understanding of excitons is crucial. This ultimately relies on the access to the correlated exciton wavefunction, which has hardly been realized in experiments. In this presentation, I will introduce the concepts of time-resolved photoemission orbital tomography and how it can be used to directly probe correlated exciton wavefunctions.

I will demonstrate the power of this technique at the example of the prototypical organic semiconductor C60, unraveling the exciton’s multiorbital electron-hole contributions [1]. Building upon this, I will present our results on the ultrafast exciton dynamics of the organic molecule PTCDA adsorbed on monolayer WSe2 [2]. By examining their unique momentum fingerprints, we can unambiguously identify the different excitonic states formed after optical excitation of WSe2. Notably, our findings reveal a hybrid exciton state characterized by concomitant intra- and interlayer electron-hole transitions within the molecular layer and across the 2D-organic interface, respectively, which gives rise to an exciton wavefunction with a mixed Frenkel-Wannier character.

References

[1] W. Bennecke, A. Windischbacher, D. Schmitt, J. P. Bange, R. Hemm, C. S. Kern, G. D‘Avino, X. Blase, D. Steil, S. Steil, M. Aeschlimann, B. Stadtmueller, M. Reutzel, P. Puschnig, G. S. M. Jansen, S. Mathias, Disentangling the multiorbital contributions of excitons by photoemission exciton tomography, Nature Communications 15, 1804 (2024)

[2] W. Bennecke, I. Gonzalez Oliva, J. P. Bange, P. Werner, M. Merboldt, A. M. Seiler, K. Watanabe, T. Taniguchi, D. Steil, R. T. Weitz, P. Puschnig, C. Draxl, G. S. M. Jansen, M. Reutzel, S. Mathias, Hybrid Frenkel-Wannier excitons facilitate ultrafast energy transfer at a 2D-organic interface, arxiv:2411.14993 (2024)