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<div style="font-family:times new roman,new york,times,serif;font-size:12pt">Seminarios DQIAQF - INQUIMAE, jueves 15 de diciembre - 13 hs.<br><br>Aula de Seminarios INQUIMAE - DQIAQF<br>Facultad de Ciencias Exactas y Naturales<br>
Ciudad Universitaria - Pab. 2 - Piso 3<br><br><br>Femtosecond electron diffraction: heralding the era of atomically-resolved dynamics</div><div style="font-family:times new roman,new york,times,serif;font-size:12pt"><br>
Germán Sciaini<br>Max Planck Research Department for Structural Dynamics, Center for Free Laser Science, DESY & Physics Department, University of Hamburg.<br><br>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.<br>
1- G.
Sciaini & R.J.D. Miller, “Femtosecond Electron Diffraction: Heralding the Era of Atomically-Resolved Dynamics”. Rep. Prog. Phys. 74, 096101 (2011).<br>2- M. Harb et al., “Electronically Driven Structure Changes of Silicon Captured by Femtosecond Electron Diffraction”. Phys. Rev. Lett. 100, 155504 (2008).<br>
3- G. Sciaini et al., “Electronic acceleration of atomic motions and disordering in Bismuth”. Nature 458, 56 (2009).<br>4- R. Ernstorfer et al., “The Formation of warm dense matter: experimental evidence for electronic bond hardening in Gold”. Science 323, 1033 (2009).<br>
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).<br><br><br><br><br> </div>
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