Thermal Transport in Copper and Manganese Oxides: Lattice Interactions and the Superconducting and Magnetic Phase Behavior

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w:\awards\awards96\*.doc 9631236 Cohn This research involves systematic experimental studies of lattice and electronic transport in doped transition metal oxides of perovskite-like structure. The goal of these studies is to elucidate and model the role of lattice vibrations in determining the superconducting and magnetic phase behavior in these materials, particularly in the copper and manganese oxides. Thermal conductivity and thermopower will be employed as probes of interactions between the lattice and the charge and spin degrees of freedom. The evolution of these interactions with charge-carrier doping and their dependence on temperature and magnetic field are a central focus of this research. Analogue systems with similar crystal structure, but with transition metals other than copper and manganese, have been selected as "controls" in these studies. These include ruthenium and nickel oxide compounds for which the strength of electron-lattice and electron-electron interactions appear to be very different %%% This research focuses on the physics of electronic and thermal conduction in transition metal oxides, a broad class of materials that have attracted considerable attention in recent years both for the novel physics their properties manifest, and for their potential use in future technologies. Of particular interest in this study are the interactions which control the superconducting and magnetic phase transitions in the copper and manganese oxides, respectively. These transitions vary with charge-carrier concentration in systematic ways within each class of materials. Signatures of the mechanisms underlying these phase behaviors will be sought in the temperature and magnetic field dependencies of the thermal transport properties, where some anomalies have already been identified. ***