Theoretical study of anomalous fluctuation and it's effects on dynamical properties of one-dimensional conductors

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In collaboration with the experimental group, we directly observed the density of state of carbon nanotubes by the photo emission study. It was shown that Tomonaga-Luttinger liquid state is realized in the carbon nanotubes in the wide range of the temperature from 10 K to room temperature. The nano-graphite ribbons are known to have the anomalous dispersion relation near the Fermi energy different from the usual metals. We investigated the electronic correlation of the materials. It was shown that the mutual interaction leads to Mott insulating ground state and the spin excitation becomes gapless (gapped) for the odd (even) number of zigzag chains.2.Splitting of the Knight shift and of the NMR relaxation rate have been considered to be the experimental evidence of charge ordering in the molecular conductors. In the case of quarter-filling, however, no one show theoretically that the charge ordering leads to such phenomena. In the present study, we calculated the Knight shift and the NM … More R relaxation rate in the pure charge ordered state of one-dimensional extended Hubbard model. Here, the fluctuation around the mean-field solution is taken into account by RPA. It is shown that the both quantities show splitting under the charge ordering, as has been already insisted. In addition, the amount of charge disproportionation estimated from the NMR experiments becomes larger than the actual value.3.Quite recently, the materials with incommensurate decomposition ratios close to 2:1 such as (MDT-TSF)_2X_n, (MDT-ST)_2X_n, and (MDT-TS)_2X_n with X being a monovalent anion and n=0.42〜0.45 have been synthesized and the transport and magnetic properties of these compounds have been measured. The materials (MDT-TSF)_2X_n and (MDT-ST)_2X_n show metallic conduction and undergo the superconducting transition at 4 K for ambient pressure. On the other hand, (MDT-TS)_2(AuI_2)_<0.441> shows the metal-insulator transition at 85 K. In order to clarify why the metal-insulator transition occurs in the case of incommensurate band filling, we investigated the ground state of one-dimensional extended Hubbard model with incommensurate lattices. When the potential from the anions is taken into account, the ground state is Mott insulator, and the increase of band width leads to metal-insulator transition. These results will qualitatively explain the experimental observation shown above. Less