Control of the Electronic State of Co Oxides and Studies on Novel Superconductivity

人们已经合成了许多具有强相关电子的系统，并对它们的物理性质进行了研究，以发现“不寻常”或“异常”的物理性质，这些物理性质有助于发展新的物理概念。在研究中，我们首先合成材料并对其进行表征，然后对其宏观性能进行研究。如果它们似乎具有物理上的吸引力，则应用核磁共振和中子散射等实验方法对其进行进一步的微观研究，其中使用了过去二十年在高to Cu氧化物研究中积累的知识作为工作的指导方针。在显微研究中，我们经常使用自己制备的单晶，这使得我们有可能获得相当可靠的实验结果。我们可以取得重大成就的主要问题是；(1) Cu氧化物高t超导电性研究中有待解决的几个问题，(2)N…More a_xCo0_2 yH_2O （y ~ 3）的超导机理，(3)Nd_2Mo_2O_2和自旋玻璃体系等非平凡磁性结构中观察到的反常霍尔效应的异常行为，(4)焦绿石体系Hg_2Cu_2F_6S中量子自旋的自旋液态，(5)钙钛矿及相关体系中Co离子的自旋态控制，(6)在（伪）蜂窝体系中发现了自旋间隙现象和新型相变；(7)寻找多铁性并详细研究了具有简单自旋1/2 Cu^2+链的CuO_2带体系中发现的多铁性现象等。在这些系统的研究中，系统的制备或合成与发现新的物理现象密切相关。为了进一步描述这些成就，我们增加了以下例子。在超导性的研究中，我们已经证明了库珀对处于单重态，排除了许多理论工作的预测以及其他小组在同一时期进行的实验研究结果。我们给出了完整的T_c-v_Q相图（v_Q：核磁共振四极频率），并通过中子非弹性散射获得了超导体动态磁性行为的关键信息。关于Nd_2Mo_2O_7是否是由自旋手性机制引起的异常霍尔效应的唯一例子的争议，我们通过详细的中子衍射研究已经很清楚地排除了这种可能性。多铁体系LiVCuO_4的发现提供了一个具有自旋1/2的具有螺旋结构的量子自旋链的新有吸引力的例子，为详细研究多铁行为的特性提供了简单方便的方法

Many systems with strongly correlated electrons have been synthesized and their physical properties have been studied to find "unusual" or "anomalous" physical properties which are useful for development of novel physical concepts. In the studies, we synthesized materials and characterized them first, and then, studied their macroscopic properties. If they seemed to have physically attractive nature, experimental methods, such as NMR and neutron scattering, were applied to further study it microscopically, where knowledge accumulated in the past two decades in the study of high To Cu oxides were used as the guide line of the works. In the microscopic studies, we often used single crystals prepared by ourselves, which made us possible to obtain quite reliable experimental results. The main subjects on which we could make significant achievements are ; (1) several problems which remained in the studies of high-T, superconductivity of Cu oxides, (2) mechanism of the superconductivity of N … More a_xCo0_2 yH_2O (y〜3), (3) unusual behavior of the anomalous Hall effect observed in nontrivial magnetic structures such as Nd_2Mo_2O_2 and spin-glass system, (4) spin liquid state of the quantum spins in pyrochlore system Hg_2Cu_2F_6S, (5) control of the spin state of Co ions in perovskite and related systems, (6) a spin gap phenomenon and a new type phase transition found in(pseudo)honeycomb systems, (7) search for multiferroics and detailed studies of multiferroic phenomenon found in systems with CuO_2 ribbons having simple spin 1/2 Cu^2+ chains, and so on. In the studies of these systems, preparation or syntheses of the systems and finding new physical phenomena are closely connected. For the further description of the achievements, we add the following as the examples. In the study of the superconductivity, we have shown that the Cooper pairs are in the singlet state, excluding predictions of many theoretical works as well as results of experimental studies carried out in the same period by other groups. We have presented complete T_c-v_Q phase diagram (v_Q : NMR quadrupole frequency), and also obtained key information on the dynamical magnetic behavior by neutron inelastic scattering of the superconductor. On the controversy if Nd_2Mo_2O_7 is the unique example of systems which exhibit the unusual anomalous Hall effect induced by the spin chirality mechanism, we have excluded such the possibility quite clearly by detailed neutron diffraction studies. To find the realization of the chirality mechanism of the anomalous Hall effect at least in periodic system remains as the future subject Our discovery of the multiferroic system LiVCuO_4 has presented a new attractive example with spin 1/2 quantum spin chains 'with helical structure, which is simple and convenient for the detailed study on the characteristics of the multiferroic behavior Less