4KFCDW induced by long range Coulomb interactions

Abstract

By method of dielectric spectroscopy we have obtained experimental data concerning the 4k F charge density wave (CDW) associated with the charge ordering (CO) state of Wigner type in (TMTTF) 2 X conductors. A divergence of the relaxation time was found at the critical transition temperature T CO into the CO state. Below T CO a low frequency shoulder appears in the frequency dependence of the imaginary part of the dielectric permittivity. Under a moderate pressure, the peak in the real part of the dielectric permittivity, corresponding to the transition into the CO state, shifts to low temperature and broadens. The substitution of hydrogen by deuterium in TMTTF molecules results in an increase of T CO (isotopic effect). The results obtained confirm the ferroelectric character of the CO state; they also favour long range Coulomb interactions as the main driven force for the formation of this state.