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SYSD: Symposium SKM Dissertation-Prize 2019

SYSD 1: SKM Dissertation Prize

SYSD 1.3: Hauptvortrag

Montag, 1. April 2019, 10:10–10:30, H2

Beyond the molecular movie: Revealing the microscopic processes behind photo-induced phase transitions — •Chris W. Nicholson — University of Fribourg, 1700 Fribourg, Switzerland — Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany

Following a "molecular movie", i.e. the real-time position of atoms during structural changes and chemical reactions is consistently cited as a key scientific challenge, relevant not only for condensed matter physics, but also femto-chemistry and biology. However, it is the dynamics of electronic excitations that ultimately lead to atomic motion across a free energy surface and the formation and breaking of chemical bonds.

In this talk, I will present femtosecond electronic structure measurements employing a recently developed setup for time- and angle-resolved photoemission spectroscopy at 22 eV and 500 kHz. This setup enables the extension of electronic band mapping throughout the full Brillouin zone to excited states above the Fermi level, as well as tracking the evolution of states and their populations during photo-induced phase transitions. Focusing predominantly on the model transition occurring in In nanowires on a Si(111) surface, I will reveal the mechanistic insights gained from measurements in momentum space that allow an understanding of not only the microscopic electronic processes driving a structural phase transition, but also the formation and breaking of chemical bonds on the femtosecond timescale. These considerations therefore extend the molecular movie concept, and may allow for optical control of structural reactions with cross-disciplinary application.