| 研究実績の概要 |
The project initiated the creation of a new field of hybrid f-/p-electron molecular materials with novel physical properties. We synthesized new families of molecular f-electron fullerides in which the electronically-active C60 anions were combined with mixed configuration rare earths. Strong correlations dominate the electronic properties of both rare-earth cation and C60 anion sublattices. In particular, the major achievement was the chemical control of the electronic configuration of the Sm ions in Sm-doped fullerides and the tuning of the rare-earth exchange interactions, the Fermi level position (band filling) and the interfullerene separation by the isolation of the Sm-Ca-C60 ternary phases with stoichiometry, Sm(2.75-x)Ca(x)C60. Structural and electronic characterization of the new materials was undertaken both at ambient and elevated pressures.
In further work, we showed that the C60-based alkali metal salts are archetypal examples not only of molecular superconductors with the highest Tc (38 K) among all molecular systems but that they also display the highest Hc2 (>90 T) among all known 3D superconducting solids. At the same time, extension of the molecular components to include polyaromatic hydrocarbons has led to the opening of new research area of strongly correlated molecular solids with exotic properties, namely candidates of quantum spin liquid behavior. Our breakthrough work in this field will appear soon as two consecutive papers in Nature Chemistry.
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| 今後の研究の推進方策 |
Future research plans focus on discovery of new materials and isolation of new electronic ground states.
Emphasis will continue to be placed on the synthesis of new families of strongly correlated f-electron fullerides but we will also tackle more complex materials both synthetically and electronically. These will include:
(1) superconducting ternary metal fullerides. Here we will begin by synthesizing binary alkaline-earth superconductors with closed-shell alkaline-earth metal ions. We will then introduce in the metal sites configurationally active rare-earth cations to synthesize the ternary phases. In this way, we will chemically introduce the prospect of coexisting superconductivity supported by the C60-based electrons and Kondo phenomena associated with the rare earth ions. We will be attempt to probe the stability of the superconducting state with changes in the filling of the fulleride conduction band driven by configuration transitions at the lanthanide dopants, and
(2) binary actinide fullerides. The actinide chemistry of fullerenes is entirely unexplored. Our new exploratory research can lead to access of novel electronic phases with co-existing magnetic and superconducting properties.
The synthetic work will be complemented by structural and electronic characterization of the new materials both at ambient and elevated pressures. This will be achieved by employing X-ray and neutron diffraction structural characterization techniques combined with magnetic characterization using SQUID magnetometry.
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