UC San Diego

A primary focus of modern condensed matter physics concerns the study of strongly correlatedmaterials in which enhanced electron interactions give rise to emergent phenomena, such as high-temperature superconductivity. The strong electromagnetic coupling between electrons and photons makes x-rays a highly sensitive probe for investigating the emergent properties of these materials. The advent of modern synchrotron light sources significantly enhances these capabilities through the production of high-brilliance x-ray beams that offer full control over the incident photon energy, thereby enabling the detection of signals emanating from phases in which only a small number of valence electrons contribute to the scattering signal via resonant enhancement. This dissertation demonstrates how these synchrotron-based x-ray scattering and spectroscopy techniques can be utilized to study a wide range of material characteristics and electronic properties in modern condensed matter systems. The x-ray techniques are applied to the characterization of two strongly correlated systems, PrxY1−xBa2Cu3O7 and FeGe. In PrxY1−xBa2Cu3O7, x-ray absorption spectroscopy and resonant inelastic x-ray scattering are used to elucidate the effects of the substituted Pr ion on the electronic structure, non-resonant inelastic x-ray scattering techniques are employed to determine the shape of the active Cu 3d orbital hole that is responsible for the anisotropic behavior observed in transport measurements, and resonant elastic x-ray scattering techniques are used to investigate a novel three-dimensional charge order that is stabilized by the Pr substitution and is demonstrated to compete directly with the high-temperature superconducting phase. Resonant elastic x-ray scattering techniques are further utilized to probe the role of the Ge honeycomb lattice in the formation of charge order in the kagome metal FeGe, which is supported by density-functional theory calculations. Understanding and controlling the correlated phenomena in these and other quantum materials has significant implications for various technologies, including quantum computing, energy storage, and next-generation electronics.