Roles of Transition Metal d-Electrons in Electronic Properties of Organic Low-Dimensional Conductors

本研究的目的是阐明过渡金属d电子在含过渡金属离子的有机低维导体电子性质中的作用。实验研究主要集中在DCNQI-Cu盐中导电电子的性质。对dmit盐的电子性质进行了表征。对（DMeDCNQI）_2Cu重入跃迁附近的电子性质进行了研究，获得了以下重要结果：（1）实验证实了DCNQI-Cu板条中铜离子的平均价态为+4/3。(3)DCNQI-Cu盐在绝缘状态下具有沿c轴沿着的三重结构，在约8 K以下的反铁磁状态的磁结构是清楚的。(4)DMeDCNQI-Cu盐的再进入跃迁伴随着磁化率、三重结构和铜离子周围的畸变的异常。(5)在DCNQI-Cu盐的再进入转变附近，绝缘状态的特性已经存在于金属状态中。此外，低至10 T的磁场使绝缘状态稳定。(6)在dmit盐中发现了类电子和类空穴的超导电性，此外还发现了一维和二维的性质，这取决于金属离子的种类.我们阐明了DCNQI-Cu盐的电子态是用DCNQI的π电子形成的一维能带的Peierls不稳定性，铜离子的d电子形成的主要能带的Mott跃迁，铜离子的Jahn-Teller效应和“软”晶格中的电子-声子相互作用。再进入相变的微观机制至今仍是一个悬而未决的问题。

The purpose of the present study is to clarify roles of transition metal delectrons in electronic properties of organic low-dimensional conductors having transition metal ions. The experimental research was focused to investigation of properties of conduction electrons predominantly in DCNQI-Cu salts. In dmit salts characterization of electronic properties was made. Special effort was made in studying electronic properties near the reentrance transition of (DMeDCNQI)_2Cu.The followings are important results obtained in the present work: (1) The average valence of the copper ion in DCNQI-Cu slats was verified experimentally to be +4/3. (3) The magnetic structure of the anti-ferromagnetic state below about 8 K was made clear in the insulating state of DCNQI-Cu salts having the three-fold structure along the c-axis. (4) The reentrance transition in DMeDCNQI-Cu salt is accompanied with anomalies in the magnetic susceptibility, the three-fold structure, and the distortion around the copper ion. (5) Near the reentrance transition of DCNQI-Cu salts properties characteristic of the insulating state are present already in the metallic state. Furthermore magnetic fields as low as 10 T stabilize the insulating state. (6) In dmit salts both electron- and hole-like superconductivities were found. In addition both one- and two-dimensional properties were found depending on species of the metal ion.We clarified that the electronic state of DCNQI-Cu salts is described in terms of the Peierls instability in the one-dimensional band formed by pi electrons of DCNQI, the Mott transition of the band formed predominantly by the d-electrons of copper ions, the Jahn-Teller effect of copper ions, and electronphonon interactions in the "soft" lattice. It is remained unsolved to reveal microscopic mechanisms of the reentrance transition.