Soft x-ray spectroscopic studies of quasi-low dimensional and strongly correlated materials

The electronic properties of quasi-low dimensional correlated transition metal compounds were investigated using x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), and resonant inelastic x-ray scattering (RIXS). XAS and XES can be used to probe the element specific partial density of electronic states, and XAS and RIXS to probe the band structure and low energy electronic excitations. These spectroscopies are photon based, rather than electron based, which allows for charge neutral measurements. Photon spectroscopies, and RIXS in particular, show promise as complementary spectroscopies to the more common angle-resolved photoemission as probes of correlated materials, and offer a means to investigate previously inaccessible insulators. A selection of quasi-low dimensional correlated systems have been studied for the first time using this combination of spectroscopic techniques.; MoO3 is a quasi-two dimensional insulator in which the effects of reduced dimensionality has not been well explored. X-ray spectroscopy was used to measure the band structure, and revealed the predicted quasi-two dimensionality in the electronic structure. When an alkali metal is incorporated, MoO 3 can be altered into a range of quasi-low dimensional materials, one of which being the prototypical quasi-one dimensional conductor K 0.3MoO3. Spectroscopic results from K0.3MoO 3 are compared to calculated predictions of the electronic structure and results from MoO3. Strong similarities are observed, despite their vastly different bulk properties.; From another large class of strongly correlated quasi-low dimensional materials, Li2CuO2 is a quasi-one dimensional insulator with crystallographic building blocks in common with high transition temperature superconductors. Polarization dependent RIXS measurements of Li2CuO 2 show the presence of a novel two-hole electronic excitation which is interpreted in light of the Cu-Cu magnetic coupling. Lastly, BaVS 3 is a quasi-one dimensional correlated metal with a metal-to-insulator transition (MIT) that involves many competing interactions. RIXS as a function of sample temperature of Ti substituted BaTi0.02V0.98S 3 was measured, and evidence of a localizing electronic transition with similar temperature dependence as the MIT in BaVS3 was detected. This is evidence that the Ti sites do not mix electronically with the V sites strongly enough to upset the balance of competing interactions that lead to the MIT in BaVS3.