Electron and lattice dynamics in solids mapped by ultrafast x-ray methods

Thomas Elsaesser (Max Born Institute, Berlin) — March 9

Abstract :
Time-resolved structure research aims at revealing the basic mechanisms behind the spatial re-arrangement of atoms and the re-distribution of electrons. X-ray diffraction and absorption methods with a femtosecond time resolution hold a particular potential for determining transient structures at atomic length scales and, thus, have been implemented with both accelerator- and laser-driven x-ray sources.
This talk combines basic concepts of x-ray diffraction and absorption on ultrashort time scales with very recent results from studies with laser-based sources. Anisotropic acoustic phonon propagation connected with photovoltaic shift currents in the ferroelectric LiNbO3 is mapped by x-ray diffraction and shown to originate from the strong piezoelectric coupling between carriers and lattice. A combined x-ray diffraction and absorption study of the hydrogen-storage material LiBH4 reveals field-induced charge relocations and the extremely small elongations of coherent phonons in the crystal lattice. The virtual transition state involved in the Raman excitation process of phonons is characterized in detail, including a map of the electric driving forces of nuclear motion.

Biography :
Thomas Elsaesser is Director at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy in Berlin. He is Professor at the Humboldt University. Thomas is an expert of ultrafast phenomena in condensed matter physics (molecular liquids, polyatomic molecules, organic and inorganic solids and nanostructures). He was awarded multiple prizes for his contribution to spectroscopy and the Innovation Prize Berlin Brandenburg for his femtosecond x-ray plasma source.

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