Title: Time-resolved photoemission orbital tomography

Time: 2023-10-11 14:30

Lecturer:  Prof. Ulrich Höfer

Philipps University of Marburg, University of Regensburg

Venue: Lecture Hall, No.3 Building,TAN KAH KEE Laboratory,Xiang’an Campus

Room 202, Lecture Hall, Lu-Jiaxi Building, Siming Campus

Abstract：

Photoemission orbital tomography (POT) is a powerful technique, by which the electron distribution in orbitals of well-ordered molecules at solid surfaces can be imaged in momentum space. Combined with laser-pump probe techniques, the method cannot only be used to investigate the dynamics of charge transfer processes at molecular interfaces. Time-resolved photoemission orbital tomography (tr-POT) also has unique potential to take slow motion videos of bond formation processes at surfaces.

In this talk, I will first review the basic principles of POT and then discuss first results obtained by trPOT. For the model system PTCDA/Cu(100)-2O, we have revealed two distinct excitation pathways with visible light. While the parallel component of the electric field makes a direct HOMO-LUMO transition in PTCDA, the perpendicular component transfers a substrate electron into the molecular LUMO. Once excited, the LUMO decays with a lifetime of 250 fs, independent of the excitation pathway. A promising strategy to time-resolve surface bond formation with the method, is to drive the molecular frame with the strong electric field of THz pulses and to perform POT with subcycle time resolution.

Bio of Prof. Ulrich Höfer:

Ulrich Höfer received his doctoral degree in physics in 1989 from the Technical University of Munich, Germany. After spending two years as a visiting scientist at the IBM Watson Research Center in Yorktown Heights, New York, he joined the Max-Planck-Institute for Quantum Optics in Garching/Munich, as a group leader. In 1999, he became a full professor for experimental physics at the Philipps University of Marburg. Since 2022, he is also adjunct professor of the University of Regensburg. Presently, he is serving as the chair of the surface science division of the German Physical Society. Höfer’s main research interests are ultrafast processes at surfaces and interfaces. He is a pioneer of time-resolved ARPES (angle-resolved photoemission spectroscopy) and coherent light-matter interaction at surfaces. His awards include the Arnold Sommerfeld prize of the Bavarian Academy of Sciences and a Synergy Research Grant from the European Research Council (ERC).