Optical studies of quasi-two-dimensional organic metals (EDT-TTF)-=SUB=-4-=/SUB=-[Hg-=SUB=-3-=/SUB=-I-=SUB=-8-=/SUB=-]-=SUB=-1-x-=/SUB=- (x=0 and 0.027) --- comparative analysis within the "phase phonons" model

Abstract

Reflection spectra of quasi-two-dimensional organic conductors (EDT-TTF)4[Hg3I8]1-x, are considered, which, depending on the composition, demonstrate different phase transitions: x=0.027 --- metal-superconductor with Tc= 8.1 K, x=0 --- metal-insulator at a temperature of T<35 K. The polarized reflection spectra were analyzed using the "phase phonons" model, which takes into account the electronic-vibrational interaction. Using this model, the optical functions of both compounds were adequately described and the energy parameters of the π--electron system were obtained. It is shown that for the compound with x=0.027 these parameters change monotonically with temperature, while for x=0 they show a jump at the phase transition temperature. A comparison of the model parameter Delta (the value of the periodic potential) for crystals with different stoichiometric coefficients x=0 and x=0.027 was carried out and an assumption was made about the dependence of the periodic potential on the average charge of one EDT molecule. Keywords: organic conductors, EDT-TTF, layered structure, reflection spectra, "phase phonons" model, electronic-vibrational interaction, optical conductivity.