报告题目：Time-resolved photoemission: From bandstructure to orbital movies
报告人：Ulrich Höfer，Philipps University of Marburg
Time-resolved photoemission combines femtosecond pump-probe techniques with angle-resolved photoelectron spectroscopy (ARPES). Recent developments enable the method to track electron motion in two-dimensional momentum space on ultrafast time scales. This capability allows exploring ultrafast electronic processes of a variety of novel quantum materials by clear-cut experiments. In this talk, I will briefly introduce the state-of-the-art of the method and discuss a couple of examples from our recent work. These include bandstructure movies of the intraband acceleration of electrons in topologically protected Dirac surface states [1,2], of the birth and collapse of Floquet-Bloch states , and of the formation of momentum-forbidden and spin-forbidden dark excitons in TMDC monolayers . Finally, I will outline the perspectives of photoemission orbital tomography  to take slow-motion movies of molecular orbitals while they are driven by lightwaves.
 J. Reimann et al., Nature 562, 396 (2018)
 C. P. Schmid et al., Nature 593, 385 (2021)
 S. Ito et al., Nature 616, 696 (2023)
 R. Wallauer et al., Nano. Lett. 21, 5867 (2021)
 R. Wallauer et al., Science 371, 1056 (2021)
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 an adjunct professor of the University of Regensburg. 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).