Dielectric Response of the Charge Ordered State in Quasi-One-Dimensional Organic Conductors

Abstract

We present a survey of the recent experimental results which provide the evidence for the formation in quasi-one-dimensional (Q1D) conductors of a charge ordered (CO) state corresponding to an electronic 4 k F charge density wave. The main attention is paid to the study of the dielectric response of Q1D organic compounds of the family of (TMTTF) 2 X salts for which a divergence of the dielectric permittivity and of the relaxation time at the critical transition temperature into the CO state are found. Effects of pressure and deuteration on this transition and also the role of anions in the formation of the CO state are studied. On the basis of these results and existing theoretical approaches we suggest a phenomelogical explanation of the sequence of ground states developed in these compounds with decreasing temperature. The driven force for the formation of the CO state originates from strong electron correlation effects associated with long range Coulomb interactions. The stability of the CO state in (TMTTF) 2 X compounds is expected to be provided by a shift of anion chains as a whole. A short comparison between peculiarities in the dielectric response of the CO state formation in Q1D and recently found in Q2D compounds will be given.