Speaker: Ulrich Hoefer
Time: Sep 19 2019 :: 2:00PM - 3:00PM
Time-resolved photoelectron spectroscopy combines femtosecond pump-probe techniques with angle-resolved photoelectron spectroscopy (ARPES). I will show how this method can be used to perform measurements of electron transport at surfaces and interfaces in a contact-free fashion and with femtosecond time-resolution [1-3]. As the main example, I will discuss Dirac surface states of topological insulators. We induce electrical currents in these states with strong THz transients and directly access their dynamics in momentum space with subcycle time resolution. As a result of spin-momentum locking, the accelerated spin-polarized electrons reach ballistic mean free paths of several hundreds of nanometers. Our results show that topological insulators are promising materials for future lightwave-driven electronics operating at THz clock rates .
 J. Güdde, M. Rohleder, T. Meier, S. W. Koch, and U. Höfer, Science 318, 1287 (2007).
 K. Kuroda, J. Reimann, J. Güdde, and U. Höfer, Phys. Rev. Lett. 116, 076801 (2016).
 J. Reimann, S. Schlauderer, C. P. Schmid, F. Langer, S. Baierl, K. A. Kokh, O. E. Tereshchenko, A. Kimura, C. Lange, J. Güdde, U. Höfer, and R. Huber, Nature 562, 396 (2018).
Ulrich Höfer received a doctoral degree in physics in 1989 from the Technical University of Munich, Germany. After spending two years as a visiting scientist at the IBM Thomas J. Watson Research Center in Yorktown Heights, New York, he joined the Max-Planck-Institute for Quantum Optics in Garching, Germany. In 1999 he became a full professor for experimental physics at the Philipps University in Marburg. His main research interests are laser spectroscopy of surfaces and interfaces, coherence and ultrafast phenomena at surfaces, and the dynamics of elementary adsorbate reactions. Since 2013 he is the spokesman of a collaborative research center on the structure and dynamics of internal interface