Low-dimensional electronic states and electron coorelation in organic conductors

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The purpose of the present research is to clarify characteristic properties of low-dimentional electronic systems in organic conductors in the light of the Coulomb correlation between conduction electrons. Research results are summarized in two points : (1) We established the important role of high magnetic fields in studying low-dimensional electronic properties, and clarified a wide variety of electronic properties caused by the magnetic fields and theoretical basis for these phenomena. (2) We made clear the physical mechanism for a novel metal-insulator transition in some organic conductors.In the study on one-dimensional electronic properties based on TMTSF molecule it was clarified that various features of magnetoresistance as a function of the angle between the magnetic field direction and the crystalline axis are explained basically by the semi-classical theory based on the band theory and the Boltzman equation. This results gave a common basis for the study on two-dimensional e … More lectronic systems described below. With respect to the possible internal phase structure in the spin-density wave state caused by the one-dimensionality and the electron correlation our original idea to investigate this from the view point of the single particle transport under high magnetic fields revealed that a band structural change caused the change in the electronic structure in the spin-density wave state.Electronic properties of the two-dimensional systembased on BEDT-TTF molecules were studied by measurements of the angle-dependent magnetoresistance oscillations under high pressures to made clear the origin of the so-called anomalous state appearing at low temperatures. In addition we found the presence of three-dimensionality causes an anomalous increase of magnctoresistance for the magnetic filed close to the conducting plane.The metal-insulator transition in one-dimensional DCNQI conductors was found to be due to interplay among the Peierls transition of one-dimensional system, the Mott transition of highly correlated system, the Jahn-Teller effect around the copper ion, magnetic spins of copper 2*state and their entropy. Less