Speaker
Description
The extreme versatility of low-dimensional materials and their combinations in hetero¬structures offers access to emergent material properties and control of microscopic processes and their dynamics. A basic understanding of the underlying physics asks for an ultrafast technique providing a quantum-state-resolved picture of many-body excitations, which requires resolution in momentum, energy, and time.
Atomically thin layered van der Waals heterostructures feature exotic and emergent optoelectronic properties. Using time- and angle-resolved photoemission spectroscopy (trARPES) combined with momentum microscopy, we investigated the excitonic dyna¬mics of the building block WSe2 and reconstructed the wavefunction of the lowest-lying bright exciton in real space [1]. In a monolayer WSe2/graphene heterostructure, we provide a layer- and momentum-resolved view of ultrafast interlayer electron and energy transfer and identify a new interfacial energy transfer mechanism governing the transfer of excitons from WSe2 to graphene [2]. This Meitner-Auger-type process complements Förster- and Dexter-typer processes and is expected to dominate the interfacial dynamics in a range of van der Waals heterostructures.
Nanoplasmonic structures can be realized by interfacing 2D semiconductors with metallic systems. By combining femtosecond electron diffraction with trARPES, we have explored the photogeneration of spin and charge currents in the nanoplasmonic structure WSe2/Au. Our techniques allow characterizing the energy flow between the two materials in terms of charge transfer, exciton formation and recombination, and subsequent decay in phononic excitations.
Furthermore, we analyze the exciton dynamics in the pentacene, were the optically prepared singlet exciton splits into two triplet excitons, in a process called singlet fission. Using trARPES we distiguish the participating excitons, which show different signatures in momentum space depending on their degree of (de)localization and their orbital character. Furthermore, these signatures enable us to disentangle the signals of energetically overlapping states and to gain mechanistic insights into singlet fission. We establish a mechanism in which low-lying charge-transfer states bridge the singlet and triplet manifolds in a single step with only a minor role of nuclear motions.
References
[1] S. Dong et al., Natural Sciences 1, e10010 (2021).
[2] S. Dong et al., arXiv:2108.06803 (2021).
[3] A. Neef et al., arXiv:2204.06824 (2022).
| Abstract Number (department-wise) | PC 02 |
|---|---|
| Department | PC (Wolf) |
