Transport and Magnetic Studies of Phase Separation and Electron Correlations in Magnetic and Superconducting Oxides

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This individual investigator award is to a young professor at the University of Miami for an experimental research project that focuses on the phenomenon of electronic phase separation in charge-carrier-doped antiferromagnetic (AF) manganites and cuprates. Electron-doped manganites, for example Ca(1-x)La(x)MnO(3) (x = 0.2), have been shown through preliminary data to be model systems for testing theoretical predictions of phase separation and are targeted for further study. The research on cuprates is motivated by a hypothesis that attributes anomalous phonon damping in AF YBa(2)Cu(3)O(6+x) to local lattice distortions induced by charge-stripe dynamics in the phase-separated CuO(2) planes. Of particular interest for the proposed work are compositions near the insulator-superconductor phase boundary (x~0.3-0.4), where the development of charge-stripe order competes with long-range Neel order. Complementing these investigations of inhomogeneous materials will be parallel studies of the layered superconductor Sr(2)RuO(4). Experiments are proposed to test the limits of applicability of Fermi-Liquid theory to this highly correlated, anisotropic system. The proposed work is expected to significantly enhance the understanding of the interplay between spin, charge, and lattice excitations that determine the novel physical properties of transition-metal oxides. The young scientists involved with this project, undergraduate students through postdocs, will receive training that will enable them to compete for future positions in academia, government, or industrial laboratories. %%%This individual investigator award is to a young professor at the University of Miami for an experimental research project that focused on the investigation of transport (electrical and heat conduction, thermoelectric effects) and magnetism in transition-metal oxide compounds that are of significant intellectual and technological interest. Three classes of compounds (manganites, cuprates, and ruthenates), that exhibit magnetism and/or unconventional superconductivity, have been targeted for study. The manganites and cuprates are systems where the physical properties can be controllably altered by adding charge carriers (doping) via chemical substitution. An important theme for this program is the phenomenon of electronic phase separation (PS), wherein the charges doped into insulating antiferromagnetic compounds segregate into nano-scale clusters. This small-scale inhomogeneity appears to be intrinsic to these materials and may prove significant for technological development, given that recent experiments and theory suggest PS is an important ingredient in the mechanisms for colossal magnetoresistance and high-temperature superconductivity. The young scientists involved with this project, undergraduate students through postdocs, will receive training that will enable them to compete for future positions in academia, government, or industrial laboratories.***