Anomalous metallic state of the one-dimensional molecular conductor (EDO-TTFBr₂)₃I₃

The structure and physical properties of the one-dimensional (1D) molecular conductor (EDO-TTFBr₂)₃I₃ are reported. This salt is composed of quasi-1D uniform stacks of the donor molecules and counter anions which are translationally disordered at room temperature. The temperature dependence of the lattice constants shows that, as the temperature decreases, the thermal contraction takes place along the donor columns, leading to the enhancement of the one-dimensionality of the π-electron system. The electrical conductivity and thermoelectric power show a metallic conductivity down to circa 140 K, where a metal-insulator transition takes place. The transition temperature decreases to circa 60 K as the hydrostatic pressure is applied up to 1.1 GPa. Although the transport properties give the itinerant feature of the π electrons, the static susceptibility behaves as a 1D Heisenberg antiferromagnetlike behavior of localized spins from room temperature down to 15 K, which is consistent with the ESR linewidth governed by the 1D diffusion mechanism of localized spins. The coexistence of the itinerant character of the transport properties and the localized character of the magnetic properties of the π-electron system is attributed to the strongly correlated nature of the quasi-1D electron system.