Metallic Properties of 1:1 Charge-Transfer Salt, Dimethyltetraselenoanthracene-Tetrafluoroborate (DMTSA-BF4)

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Abstract
Pseudo-one-dimensional charge-transfer salt DMTSA-BF 4 shows high electrical conductivity (σ RT ≈500 Scm -1 ) and metallic temperature dependence down to ca. 160 K, in contrast to the conventional half-filled organic conductors which are regarded as Mott insulators. The pseudo-one-dimensionality is evidenced by the polarized reflectance spectra. The electrical resistivity, thermopower, magnetic susceptibility, and polarized reflectance spectrum suggest that DMTSA-BF 4 is a metal above ca. 150 K. This compound is the first metal among the 1:1 organic charge-transfer salts. The low-temperature reflectance spectrum suggests that the glide plane symmetry is broken below 150 K and the fluctuation of this broken symmetry is already observed at room temperature. The metal-insulator transition around 150 K is regarded as Peierls transition. The Hubbard parameter U / W is estimated to be <0.8, which may be the possible reason for the metallic nature in high-temperature phase.