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O: Fachverband Oberflächenphysik
O 15: Mini-Symposium: Ultrafast surface dynamics at the space-time limit II
O 15.5: Talk
Monday, March 1, 2021, 15:05–15:25, R1
Tracing orbital images on ultrafast time scales — •Robert Wallauer1, Miriam Raths2,3, Klaus Stallberg1, Lasse Münster1, Dominik Brandstetter4, Xiaosheng Yang2,3, Jens Güdde1, Peter Puschnig4, Sergey Soubatch2, Christian Kumpf2,3, Francois C. Bocquet2, Frank Stefan Tautz2,3, and Ulrich Höfer1 — 1Fachbereich Physik, Philipps-Universität Marburg, Germany — 2Peter Grünberg Institut, PGI-3, Forschungszentrum Jülich, Germany — 3Jülich Aachen Research Alliance (JARA), Jülich, Germany — 4Insititute of Physics, Universität Graz, Austria
Photoemission tomography is a powerful tool to image the electron distribution in molecular orbitals in momentum space. Unoccupied molecular orbitals, however, have not been accessed until now. In our experiment, we combine time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measure the full momentum-space distribution of transiently excited electrons within a single molecular layer of PTCDA on an oxygen-passivated Cu(001) surface.
Beside the identification of the lowest unoccupied molecular orbital and its lifetime, we were able to link the excited state dynamics to real-space excitation pathways. Electron transfer from the substrate to the molecule and intramolecular excitation lead to distinct signatures in the time evolution of the respective momentum map. Our results show the potential of this technique to identify electron excitation and transfer processes at molecular surfaces and interfaces.