[Todos] Jueves 15 de diciembre - 13 hs - .Seminarios DQIAQF - INQUIMAE

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Seminarios DQIAQF - INQUIMAE,  jueves 15 de diciembre - 13 hs.

Aula de Seminarios INQUIMAE - DQIAQF
Facultad de Ciencias Exactas y Naturales
Ciudad Universitaria - Pab. 2  -  Piso 3


Femtosecond electron diffraction: heralding the era of atomically-resolved
dynamics

Germán Sciaini
Max Planck Research Department for Structural Dynamics, Center for Free
Laser Science, DESY & Physics Department, University of Hamburg.

One of the great dream experiments in Science is to directly observe atomic
motions as they occur. Femtosecond electron diffraction provided the first
‘light’ of sufficient intensity to achieve this goal by attaining atomic
resolution to structural changes on the relevant timescales. During my talk
I will cover the technical progress that made this new level of acuity
possible and give a survey of the new insights gained from an atomic level
perspective of structural dynamics (1). Atomic level views of the simplest
possible structural transition, melting, are discussed for a number of
systems in which both thermal and purely electronically driven atomic
displacements can be correlated with the degree of directional bonding
(2-4). Optical manipulation of charge distributions and effects on
interatomic forces/bonding can be directly observed through the ensuing
atomic motions. New phenomena involving strongly correlated
electron–lattice systems are also discussed in which optically induced
changes in the potential energy landscape lead to ballistic structural
changes. Concepts such as the structural order parameters are now directly
observable at the atomic level of inspection to give a remarkable view of
the extraordinary degree of cooperativity involved in strongly correlated
electron–lattice systems (5). For the delight of chemists, I will finalize
my talk showing recent results obtained for an organic crystal composed by
light scattering centers. Here, we implemented a recently developed
ultra-bright femtosecond electron source to obtain an atomically-resolved
map of the relevant molecular motions driving the photo-induced
insulator-to-metal phase transition in the organic charge-transfer salt
(EDO-TTF)2PF6. This study is the first in its kind and illustrates the
potential of ultra-bright femtosecond electron sources to provide new
insights into the physics of strongly-correlated organic solids.
1- G. Sciaini & R.J.D. Miller, “Femtosecond Electron Diffraction: Heralding
the Era of Atomically-Resolved Dynamics�. Rep. Prog. Phys. 74, 096101
(2011).
2- M. Harb et al., “Electronically Driven Structure Changes of Silicon
Captured by Femtosecond Electron Diffraction�. Phys. Rev. Lett. 100, 155504
(2008).
3- G. Sciaini et al., “Electronic acceleration of atomic motions and
disordering in Bismuth�. Nature 458, 56 (2009).
4- R. Ernstorfer et al., “The Formation of warm dense matter: experimental
evidence for electronic bond hardening in Gold�. Science 323, 1033 (2009).
5- M. Eichberger†, H. Schäfer†, G. Sciaini† et al., “Snapshots of
Cooperative Atomic Motions in the Optical Suppression of Charge Density
Waves�. (†equal contributions). Nature 468, 799 (2010).
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