Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 79: Frontiers of Electronic Structure Theory: Optical Excitation (organized by O)

TT 79.9: Talk

Wednesday, March 18, 2015, 17:15–17:30, MA 004

Inelastic X-Ray Scattering: Insights from and Benefits for Many-Body Theory — •Claudia Rödl, Igor Reshetnyak, Francesco Sottile, and Lucia Reining — Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA-DSM, 91128 Palaiseau cedex, France

Non-resonant inelastic x-ray scattering (IXS) probes the momentum- and frequency-dependent dynamic structure factor S(q,ω). It captures the neutral excitations of a many-body system, such as excitons, plasmons, and interband transitions. In particular, localized excitations that are forbidden in the optical limit of vanishing momentum transfer are accessible. S(q,ω) is proportional to the diagonal element of the electric susceptibility χ(q,q′,ω). Thus, IXS directly probes the dielectric screening and, hence, the screened Coulomb interaction which governs, for instance, the formation of quasiparticles in photoemission spectroscopy and excitons in optical spectroscopy. Therefore, IXS provides a unique tool to disentangle the many-body physics of renormalized quasiparticles and neutral excitations. It may serve as a solid experimental reference for the development of new approaches in many-body theory. Moreover, the off-diagonal elements of χ(q,q′,ω) can be probed by coherent inelastic x-ray scattering (CIXS). This technique, which is still at a pioneering stage, allows one to visualize plasmon-like and localized neutral excitations in real space. We calculate diagonal and off-diagonal elements of χ(q,q′,ω) for semiconductors and transition-metal oxides in good agreement with experiment and discuss the rich physics that is contained in χ(q,q′,ω).