Search for Novel Superconductors with High-Tc in the Ru Oxide System and Possibility for Coexistence of Magnetism and Superconductivity

寻找具有新的物理性质的新化合物是非常重要的，这可能会导致固体科学领域的突破。在这种背景下，化学家的作用在这一研究领域中变得非常重要。我们研究了各种4d和5d过渡金属氧化物系统的合成及其化学和物理性质，试图寻找具有新型量子现象的新化合物，特别是超导和金属-绝缘体过渡化合物。因此，最近发现焦绿石氧化物Cd_2RE_2O_7在约1K表现出超导电性，这是在受挫自旋系统中首次发现的超导体。我们还在Cd_2RE_2O_7中发现了类似于铜酸盐高T_c体系中自旋能隙行为的赝隙行为。我们还发现了具有有趣物理化学性质的新型化合物：EuSr_2RuCu_2O_8(铁磁和超导共存)，Tl_2Ru_2O_7(T&lt以下的金属-绝缘体转变和自旋能隙行为；M-1&GT；)，Bi2Ru_2O_7和Pb2Ru_2O_7(具有反铁磁自旋涨落的Pauli顺磁)。现在，包括自旋动力学在内的这些化合物的进一步物理性质的研究仍在详细进行中，并将在其他地方报道。

It is quite important to find out new compounds which show new physical properties, leading to a possible breakthrough in the field of solid state sciences. In this context, the role of chemists is very important in this research field.We have investigated the syntheses and chemical and physical properties of various 4d and 5d transition metal oxide systems, and tried to find new and novel compounds which show new-type of quantum phenomena, especially, superconducting and metal-insulator transition compounds.As a result, recently, the Pyrochlore oxide Cd_2Re_2O_7 has been found to exhibit superconductivity at about 1 K, which is a firstly-found superconductor in the frustrated-spin system. We also found a pseudo-gap behavior in Cd_2Re_2O_7 below T^* of about 200K which resembles the spin-gap behavior in the cuprate high-T_c systems.We have also found new-type compounds with interesting physical and chemical properties in this research program as follows: EuSr_2RuCu_2O_8 (coexistence of ferromagnetism and superconductivity), Tl_2Ru_2O_7 (Metal-Insulator transition and spin-gap behavior below T_<M-1>), Bi_2Ru_2O_7 and Pb_2Ru_2O_7 (Pauli paramagnetism with antiferromagnetic spin fluctuations). Now, further study of physical properties of these compounds including spin dynamics is still in progress in detail, and will be reported elsewhere.