DMET, dimethyl(ethylenedithio)diselenadithiafulvalene is the first unsymmetrical donor that gives an organic superconductor. Among the conducting DMET salts, (DMET)_2Au(CN)_2, (DMET)_2AuI_2, (DMET)_2AuC1_2, (DMET)_2I_3, (DMET)_2IBr_2, (DMET)_2AuBr_2 and (DMET)_2SCN are quasi-one-dimensional metals at ambient pressure. Although the crystal structures of the salts are isostructural, the salts have different low temperature phases. Some of them undergo metal to superconductor or semiconductor transition at low temperature, while the others remain in the normal metallic state. Thermopower was measured for the salts along the highest conducting direction. Transfer integral, t(4t=bandwidth) of the salts was determined from the temperature dependence of the thermopower. Dimensionality of the electronic system in the salts was estimated from the transfer integral and their crystallographic data. It was found that the difference in the low temperature phases can be explained by the relatively high dimensionality of the salts that undergo the superconducting transition. To estimate the dimensionality by the fully experimental method, the anisotropy of magnetoresistance was measured for (DMET)_2Aut_2, (DMET)_2I_3 and (DMET)_2AuBr_2 along the least conducting direction for the magnetic field perpendicular to the electrical current. The measurement was alto carried out for the (DIMET)_2I_3 for the comparison with the DMET salts, where DIMET is an abbreviation of dimethyl(ethylenedithio)tetrathiafulvalene and (DIMET)_2I_3 is isostructural to the DMET salts. The phase transition induced by the magnetic field was suggested for (DMET)_2I_3 and (DMET)_2AuBr_2 by the change in the angular dependence of the magnetoresistance at low temperature. It was found that the estimation of the dimensionality from the magnetoresistance is difficult due to the possible phase transition, at least, among the DMET salts. (DMET)_2BF_4, (DMET)_2ClO_4 and (DIMET)_2BF_4 have the novel crystal structure, where two types of quasi-one-dimensional donor columns are almost perpendicular to each other. To characterize their physical properties, resistivity by Montgomery method and thermopower along the each column were measured for the salts. Plural phase transition were found in the semiconducting sate below the metal-semiconductor transition temperature for all the salts. To know about the nature of the phase transitions, the angular dependence of the magnetoresistance along the direction perpendicular both to the two kinds of columns was measured for (DMET)_2ClO_4. The mechanism of the phase transitions was discussed. The transport properties of organic conductors based on DMET analogs, DIMET and ETDM, ethylenedithio(dimethy1)diselenadithiafulvalene were investigated by the measurement of the resistivity and thermopower at ambient pressure and under hydrostatic pressure. For the sake of a guidance to get a new organic superconductors the comparison among the physical properties of the salts based on DMET and its analogs was carried out.東京都立大学, 1995-03-25, 博士(理学), 甲第357
