Novel Electronic States in the Soft Lattice of Organic Conductors from the Control to the Design of Electronic States

有机导体是柔软的，晶体结构不仅会发生分子位置的变化，而且会发生分子取向的变化。本研究的目的是揭示在“单轴压缩”结构控制下，低温下有机导体晶体结构变化与电子性能之间的关系。这导致了有机化合物的控制和设计，这些化合物具有丰富多样的结构和电子性质。我们成功地开发了单轴压缩输运和低温x射线衍射测量的实验方法。用这种方法测量了准二维导体α-(BEDT-TTF)_2XHg(SCN)_4 （X=K和X=NH_4）的电阻、磁电阻和低温晶体结构。在超导性方面，我们发现在平行于c轴的单轴压缩下，超导临界温度从环境压力的1.5K增加到6K。通过x射线结构分析得到的电子结构与BCS理论对临界温度的理论预测在半定量上一致。这一结果首次证明了单轴压缩方法的可行性。在静水压力下的研究中，我们还发现了一种新的磁阻现象，并将其命名为“小闭合轨道效应”。我们还测量了β型和θ型BEDT-TTF系列和BO系列有机导体等相关材料的单轴应变效应。发现电子性质的变化如预期的那样发生了。然而，我们发现了一些新的现象，需要在未来的研究中进行调查。我们还尝试了用有机受体设计材料，成功合成了原始有机超导体（BETS）_2（Cl_2TCNQ）。这是第一个完全由有机分子组成的有机超导体。本研究开发的单轴应变方法有望用于控制电子之间的库仑相关，并应用于磁和光学测量。少

Organic conductors are soft and suffer changes in crystal structure of not only the molecular position but also the molecular orientation. The purpose of this study is to reveal the relationship between changes in crystal structure and electronic properties of organic conductors at low temperature under structural controls by "uniaxial compression". This leads to a control and a design of organic compounds, which have a rich variety in structure and electronic properties.We succeeded to develop the experimental method of uniaxial compression for transport and low-temperature x-ray diffraction measurements. Using this method, we measured electrical resistance, magnetoresistance and low temperature crystal structure of quasi two-dimensional conductors α-(BEDT-TTF)_2XHg(SCN)_4 where X=K and X=NH_4. In relation to superconductivity, we found an increase in the superconducting critical temperature from 1.5K of ambient pressure to 6K under the uniaixial compression parallel to the c-axis. Th … More e electronic structure derived by x-ray structure analyses was found to be semi-quantitatively consistent with theoretical expectation for the critical temperature by BCS theory. This result remonstrated the feasibility of the uniaxial compression method for the first time. We discovered also a novel magnetoresistance phenomenon in studies at hydrostatic pressures and named it "small closed-orbit effect".We measured also uniaxial strain effects in related materials like the β- and θ-type BEDT-TTF series and BO series of organic conductors. Changes in electronic properties were found to occur as expected. However, we discovered some novel phenomena to be investigated in future studies. We tried also a material design using organic acceptors to succeed in synthesizing original organic superconductor (BETS)_2(Cl_2TCNQ). This is the first organic superconductor composed of only organic molecules.The uniaxial strain method developed in this research is expected to be useful in controlling Coulomb correlation between electrons and to be applied also to magnetic and optical measurements. Less