Low Dimensional and Correlated Solids
Correlated and low dimensional solids present important challenges to modern solid-state physics. While our knowledge of the origin the physical properties of many simple solids is both comprehensive and sophisticated, this is not the case in low dimensional and correlated solids. From quasi-low dimensional conductors, through magnetoresistive oxides, to high temperature superconductors, there exists a plethora of physical phenomena displayed by these materials that remain poorly understood. Transition metal oxide bronzes are inorganic quasi-low dimensional correlated solids that are ideal prototypical systems for spectroscopic studies, due to the large size and high quality of available crystals. Among the unusual properties of these oxides are low-dimensional electron transport, metal-insulator and metal-metal transitions, periodic lattice distortions and charge-density-wave transport. Many of these phenomena are related to the coupling between vibrational modes of the lattice with the electrons at the Fermi level. Of particular importance in this coupling is the structure of the Fermi surface itself. Despite its fundamental role, the structure of the Fermi surface in low-dimensional systems is generally undetermined. Our research program addresses numerous aspects of the physical nature of these oxides and combines the information on each topic into a coherent model for their low dimensional properties. We measure quasi-low-dimensional Fermi surfaces, metal d-band dispersion, spatial localization and hybridization of the d-electrons, bonding interactions at different sites in the lattice, the creation of energy gaps at the Fermi level, and the formation and structure of point and extended defects.