Infrared and Raman studies of quasi-one-dimensional conductors ( o-DMTTF) 2X (X=Br, I)

Abstract

Polarized IR reflectance spectra (700–16 000 cm −1) and Raman spectra for red excitation (λ=632.8 nm) of ( o-DMTTF) 2X (X=Br, I) single crystals were measured as a function of temperature ( T=10–300 K). Raman data provide evidence of uniform charge distribution in o-DMTTF stacks down to the lowest temperatures. Despite metallic behavior from dc conductivity measurements the optical conductivity data suggest the presence of an optical energy gap. The energy gaps of both compounds have been determined. Temperature dependence of both Raman and IR spectra indicates two phase transitions at about 50 and 200 K.