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L'Association Européenne de Cristallographie (ECA) organise depuis 2021 des "webinaires déjeuner". Les groupes d'intérêt spéciaux (SIG) et les groupes d'intérêt général (GIG) de l'ECA organisent à tour de rôle un webinaire adapté à la communauté des cristallographes au sens large. Le dixième webinaire sera diffusé le 7 avril 2022 (exceptionnellement à 14h) et s'inscrit dans le thème de  SIG-12 - Crystallography of Functional Materials. Le thème de ce webinaire est Understanding the influence of the crystal structure on the functional properties of complex oxides. Physical mechanisms and crystal chemistry (Nicole Benedek, Materials Science and Engineering, Cornell University, USA). Inscriptions ici.

Recent experiments have demonstrated the potential for ultrafast changes in the functional properties of materials upon selective optical excitation of particular vibrational (phonon) modes. The chemical diversity of complex oxides, and their strong crystal structure-properties coupling, have made them ideal test systems for new experimental approaches that exploit anharmonic phonon couplings to induce and modify magnetism, superconductivity and ferroelectricity with light. In this talk, I will describe our recent theoretical efforts exploring ultrafast optical control of the functional properties of ABO3 perovskite oxides. In particular, I will focus on our attempts to connect the physical mechanisms of optical excitation to crystal chemistry using two examples: dynamical stabilization of a non-equilibrium magnetic phase in GdTiO3, and understanding changes in non-equilibrium structure and properties in terms of intrinsic microscopic quantities for LaAlO3 under pressure. Our work complements recent experimental studies involving X-ray free electron lasers to resolve subtle changes in crystal structure due to optical phonon pumping, and highlights the importance of understanding the contributions of small structural distortions to the optical response in perovskites, in contrast with large-amplitude distortions, such as so-called rotations of the BO6 octahedra.


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