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Strongly correlated materials are characterized by the presence of electron-electron interactions in their electronic structure. They often have remarkable properties and transitions between competing phases of very different electronic and magnetic order. This thesis focuses on strongly correlated $f$-electron compounds containing Ce, Sm, and U. These materials exhibit a so-called heavy-fermion or Kondo-lattice behavior. They can become insulating due to hybridization effects (Kondo-insulator) or develop multipolar (hidden) order. Kondo insulators have recently been discussed in the context of strongly correlated topological insulators. This new aspect caused an enormous activity in the field of Kondo insulators, theoretically as well as experimentally. Multipolar order as well as the formation of a Kondo insulating state strongly depend on the symmetry of the $f$ states involved. Also the character of the surface states in a topological insulator is determined by the properties of the bulk states. Therefore the scope of this thesis has been to unveil the underlying symmetries of the bulk $f$ states. Here the compounds CeB$_6$, UO$_2$, and URu$_2$Si$_2$, which exhibit multipolar order, as well as the Kondo insulators (semimetals) SmB$_6$ and CeRu$_4$Sn$_6$ have been studied.
We report a high-resolution resonant inelastic x-ray scattering study of La2CuO4. A number of spectral features are identified that were not clearly visible in earlier lower-resolution data. The momentum dependence of the spectral weight and the disp
Non-resonant inelastic x ray scattering (NIXS) experiments have been performed to probe the 5d-5f electronic transitions at the uranium O(4,5) absorption edges in uranium dioxide. For small values of the scattering vector q, the spectra are dominated
We report a resonant inelastic x-ray scattering study of the dispersion relations of charge transfer excitations in insulating La$_2$CuO$_4$. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitatio
The control and detection of crystallographic chirality is an important and challenging scientific problem. Chirality has wide ranging implications from medical physics to cosmology including an intimate but subtle connection in magnetic systems, for
We analyze the resonant inelastic x-ray scattering (RIXS) spectra at the Cu and Ni K edges in La2CuO4 and La2NiO4, respectively. We make use of the Keldysh-Green-function formalism, in which the RIXS intensity is described by a product of incident-ph