PGI Colloquium:Prof. Dr. Ulrich Höfer, University of Marburg, Germany

PGI Lecture Hall, Building 04.8, 2nd Floor, Room 365

Ultrafast Views of Electron Motion at Surfaces and Internal Interfaces

Electron transfer processes at surfaces and interfaces play a crucial role in diverse fields of materials sciences. In this talk, I will discuss surfaces of three-dimensional topological insulators and interfaces between metals and organic semiconductors. Time-resolved two-photon photoemission (2PPE), a method that combines femtosecond pump-probe techniques with photoelectron spectroscopy, can provide detailed information about the ultrafast dynamics of electrons excited into surface and interface-specific states of these systems.

For investigations of metal/organic interfaces, PTCDA/Ag(111) has proven to be an excellent model system. It will be shown that the interface state, located between the Fermi level of the metal and the molecular LUMO of this and related systems, can efficiently mediate the electron transfer between the metal and the organic semiconductor.

Three-dimensional topological insulators belong to a new class of materials which are characterized by an insulating bulk and a metallic surface state with a Dirac-cone-like energy dispersion. It will be shown that mid-infrared pump pulses permit a direct excitation of the topological surface state of Sb₂Te₃ across the Dirac point. The optical coupling leads to an asymmetric transient population in momentum space which reflects a macroscopic electric surface current. By observing the population decay with time-delayed UV probe pulses, we directly access the dynamics of the photocurrent and its topologically protected properties.

Kontakt

Christian Kumpf

Telefon: +49 2461 61-1452

Fax:  +49 2461 61-3907

E-Mail: c.kumpf@fz-juelich.de