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电子在含过渡金属离子的有机低维导体的电子特性中的作用。实验主要研究了DCNQI-Cu盐中导电电子的性质。对其电子性能进行了表征。重点研究了（DMeDCNQI）_2Cu再入口跃迁附近的电子性质。本文得到了以下重要结果：(1)实验验证了DCNQI-Cu板条中铜离子的平均价为+4/3。(3)沿c轴呈三重结构的DCNQI-Cu盐在绝缘状态下，在约8 K以下反铁磁态的磁性结构清晰可见。(4) DMeDCNQI-Cu盐的再入口转变伴随着磁化率、三重结构和铜离子周围畸变的异常。(5)在DCNQI-Cu盐的再入口转变附近，绝缘态的特性已经呈现在金属态。此外，低至10t的磁场稳定绝缘状态。(6)在纳米盐中发现了类电子和类空穴超导性。此外，根据金属离子的种类，发现了其一维和二维性质。我们澄清了DCNQI- cu盐的电子态是由DCNQI的pi电子形成的一维带中的Peierls不稳定性、主要由铜离子的d电子形成的带的Mott跃迁、铜离子的Jahn-Teller效应和“软”晶格中的电子-声子相互作用来描述的。重新进入过渡的微观机制仍未得到解决。

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.