Optical, spin-resonance, and magnetoresistance studies of(tetrathiatetracene)2(iodide)3. The nature of the ground state

Abstract

Optical, spin resonance, and high-field magnetoresistance studies of the organic charge-transfer salt ${\mathrm{}\left(\mathrm{tetrathiatetracene}\right)\mathrm{}}_2$ ${\mathrm{}\left(\mathrm{iodide}\right)\mathrm{}}_3$ [${\mathrm{}\left(\mathrm{TTT}\right)\mathrm{}}_2$ ${\mathrm{I}}_3$] have been carried out. This material is a single-carrier system consisting of segregated linear chains of TTT cation radicals and tri-iodide ions which are incommensurate with respect to each other. The ${\mathrm{I}}_3^{-}$ chains exhibit considerable disorder perpendicular to the chain axis. ${\mathrm{}\left(\mathrm{TTT}\right)\mathrm{}}_2$ ${\mathrm{I}}_3$ has a high room-temperature conductivity $\sigma \left(300\mathrm{}°\mathrm{K}\right)\sim 1000$ ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ along the chain axis and is metallic down to ∼100°K where a possible phase transition occurs. The nature of this transition is discussed. Below 30°K, ${\mathrm{}\left(\mathrm{TTT}\right)\mathrm{}}_2$ ${\mathrm{I}}_3$ exhibits semiconducting properties indicating that the low-temperature ground state is nonmetallic.