Séminaire général : Matteo GATTI. Coupling of excitations. Coupling of spectroscopies
Summary: One of the great challenges of condensed-matter physics is the description, understanding, and prediction of the effects of the Coulomb interaction on materials properties. In electronic spectra, the Coulomb interaction causes a renormalization of excitation energies and a transfer of spectral weight. Most importantly, it can be responsible for qualitatively new structures, such as satellites in photoemission spectra. Being a genuine signature of dynamical correlation, they are absent in a non-interacting picture but can be understood in terms of the coupling between different elementary excitations. Their identification can lead to the discovery of new classes of functional materials. In this context, a key physical ingredient is the dynamical screening of the Coulomb interaction, containing charge excitations such as plasmons and excitons. These ideas promote a collaborative strategy based on the coupling between the spectroscopies that independently measure the various excitations, such as photoemission, electron energy loss spectroscopy and inelastic x-ray scattering (both in the resonant and non-resonant versions). In this talk, I will present some case studies where the tight interlinking between theory and experiment has been crucial for the investigation of electronic excitations in materials ranging from simple metals to transition metal oxides. Finally, since what is calculated and what is measured are often different, I will highlight the importance of bridging the gap between theory and experiment to uncover new physics. The results that will be presented have been obtained thanks to fruitful collaborations with several members of the Palaiseau Theoreticalspectroscopy group and colleagues from experimental groups.
Biography: Matteo Gatti is a CNRS researcher at the Laboratoire des Solides Irradiés of the Ecole Polytechnique, research team leader of the European Theoretical Spectroscopy Facility (ETSF), and associated researcher at the Synchrotron SOLEIL. His research activities are devoted to the development of theoretical and numerical approaches for the calculation of many-body effects in electronic spectra of materials, in a strong synergy with experiments. A wide range of applications, from photovoltaics to cultural heritage, often combine fundamental questions and technological interests.