Peierls structural transition of TTF-TCNQ organic crystals in the 2D physical model

Abstract

Many quasi-one-dimensional (Q1D) organic crystals, known as synthetic metals at room temperature, become insulators when the temperature decreases, due to the Peierls transition. In the last years, it was demonstrated theoretically, that after the optimization of parameters, the organic crystals of TTF-TCNQ (tetrathiofulvalene-tetracyanoquinodimethane) are good candidates for thermoelectric materials. Peierls transition in Q1D crystals of TTF-TCNQ type is studied in a 2D physical model of the crystal. There are considered two the most important electron-phonon interactions. The equation for phonon Green function is deduced in the random phase approximation as a sum of diagrammatic ladder series of close loops of electronic Green functions. The polarization operator as a function of temperature is calculated for different values of the parameter δ, where δ is the increase of the Fermi momentum, kF , that is determined by the increase of carrier concentration. The Peierls critical temperature Tp was determined for different values of δ.