The theory for the ferroelectric Mott–Hubbard phase in organic conductors

Abstract

Discoveries of the ferroelectric (FE) anomaly (Nad, Monceau, et al.) and the related charge disproportionation (S. Brown et al.) call for a revaluation of the phase diagram of the (TMTTF) 2X compounds and return the attention to the interplay of electronic and structural properties. We shall describe a concept of the combined Mott–Hubbard state as the source for the ferroelectricity. We shall demonstrate the existence of two types of spinless solitons: the π-solitons, the holons, are observed via the activated conductivity; the noninteger α-solitons are responsible for the depolarization of the FE order. We propose that the (anti) ferroelectricity does exists hiddenly even in Se subfamily, giving rise to the unexplained yet optical peak. We remind then the abandoned theory by the author and Yakovenko for the universal phase diagram which we contrast with the recent one.