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

Optical, spin resonance, and high-field magnetoresistance studies of the organic charge-transfer salt (tetrathiatetracene)2(iodide)3 [(TTT)2I3] 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 I3- chains exhibit considerable disorder perpendicular to the chain axis. (TTT)2I3 has a high room-temperature conductivity (300°K)1000 -1cm-1 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, (TTT)2I3 exhibits semiconducting properties indicating that the low-temperature ground state is nonmetallic.