A study on cooperation and competition between the magnetic correlation and transport properties in systems with localized and itinerant electrons

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In this program, we systematically studied cooperation or competition between magnetic order or fluctuation and superconductivity of strongly correlated electron systems such as high temperature superconductors and uranium compounds by using neutron scattering and other microscopic techniques on single crystals with high quality.The superconductivity in the high temperature cuprates appears by carrier doping into the Mott insulators. In recent years, the self-organization of the doped carriers was found in these cuprates particularly in the 2-1-4 type cuprates. One of the main issues is whether the self-organization commonly occurs in other types of cuprates and induces novel quantum properties such as high temperature superconductivity. Although this issue is still continuing, in this program we could provide several key experimental results for the elucidation of this problem.In the study on the uranium compounds particularly on UPd_2Al_3 , we completed a model for the paring mechanism, where three 5f-electrons of U play a role differently for the superconductivity in this compound ; one constructs a magnetic framework and the other forms the Cooper paring through the magnetic excitations of the framework. It turns out this model can explain not only the symmetry of the superconductivity also many of the physical properties of this system.As seen in UPd_2Al_3 the possibility of contribution from different types of electrons for mechanism of the paring force in the high temperature superconductor will be one of the main issues and elucidated if one succeeds in distinguishing the intrinsic electronic inhomogeneity from that caused by the chemical randomness by doping carriers.