How atoms and charges move in crystals x-ray diffraction in the femtosecond time domain
Thomas Elsaesser (Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy)

Infos Complémentaires

Salle E244 - 24, rue Lhomond - 13h30

Jeudi 11 octobre

Numerous functional processes in condensed matter involve atomic motions and
charge relocations on ultrashort time scales. X-ray diffraction methods with a femtosecond
time resolution allow for spatially resolving transient structures and charge
distributions in a most direct way, providing new insight into the structure-function
relationship of crystalline materials. This talk combines an introduction into this
research field and its methods with a discussion of recent results on structural
dynamics of ionic crystals. Optical pump/ x-ray probe experiments with laser-driven
hard x-ray sources reveal the interplay of lattice and charge motions in the photoexcited
prototype material KDP (KH2PO4). Elongation of the soft mode, a lowfrequency
lattice vibration, induces an electron relocation over the length of a PO
bond which is 100 times larger than the underlying vibrational amplitude. This
behavior is caused by the strong electric forces the oscillating ions exert on the
highly polarizable valence electrons of the phosphate groups. As a second
example, the field-driven transfer of valence electrons between ions in a superposition
of quantum states of LiBH4 will be addressed.

Salle E244 - 24, rue Lhomond - 13h30