CONTROL OF ELECTRONIC STATES OF ORGANIC SUPERCONDUCTORS BY UNIAXIAL STRAIN METHOD

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This research aims to reveal the relationship among superconductivity and various types of electronic state of organic superconductors by uniaxially compressing crystalline lattices only along the desired direction and controlling their crystal and electronic structures.In a series of organic conductors having a quarter-filled conduction band with the strong Coulomb correlation, the relationship among the metallic, charge-ordered, and superconducting states were clarified by systematic investigations of electrical transport properties, crystal and electronic structures under the uniaxial strain. We found that the band structure predominated the electronic state of α-(BEDT-TTF)_2XHg(SCN)_4, (X=K,NH_4). In θ-(BEDT-TTF)_2CsZn(SCN)_4,the newly synthesized α-(BEDT-TTF)_2CsCd(SCN)_4 and β-(BEDT-TTF)_2CsCd(SCN)_4,and β''-(DODHT)_2PF_6 synthesized by the Tokyo Metropolitan University group, however, their electronic states were found to be dominated by the charge ordering due to the long range … More Coulomb correlation. These results lead to a unified phase diagram of the electronic states of α-,θ-and β-types of organic conductor, In the half-filled band system, K-(BEDT-TTF)_2X [X=Cu(NCS)_2,Cu[N(CN)_2]Br,Cu_2(CN)_3] the on-site Coulomb correlation causes the Mott insulating state. We found that the deformation of their triangular lattice by the uniaxial compression controlled the electronic states and the spin-firustrating state to realize an increase in the superconducting critical temperature and a nonmagnetic spin state. These results suggested the importance of the spin fluctuations for the mechanism of superconductivity.In the development of new materials, we turned our attention to the intermolecular interaction of the iodine bonding and the hydrogen bonding of CH・・・O type to make the supramolecular structure that gives rise to new supramolecular conducting and superconducting materials. We developed a safe method to synthesize [1,3] diselenole derivative that served as a basic reagent for new materials syntheses and succeeded in synthesizing TTF derivatives having selenium. We developed also a series of crystals of supramolecular organic conductors that had effective arrangements of anisotropic molecular interactions based on the iodine bonding. We succeeded in synthesizing BEDO-TSeF, the last unexplored molecule belonging to the family of BEDT-TTF derivative and clarifying its basic structural and electronic basic properties. Less