The Impact of Discoveries of Ferroelectricity and Charge Disproportionation in Organic Conductors

TL;DR

This paper reviews recent discoveries of ferroelectricity and charge disproportionation in organic conductors, proposing a new combined Mott-Hubbard state model and identifying different types of solitons affecting ferroelectric properties.

Contribution

It introduces the concept of a combined Mott-Hubbard state as the origin of ferroelectricity and identifies two types of spinless solitons influencing electronic and ferroelectric behavior.

Findings

Existence of two types of spinless solitons: pi- solitons and alpha- solitons.

Hidden ferroelectricity in the Se subfamily suggested by optical peaks.

Reevaluation of the phase diagram of (TMTTF)2X compounds.

Abstract

Discoveries of the Ferroelectric anomaly (Nad, Monceau, et al) and of the related charge disproportionation (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: pi- solitons, the holons, are observed via the activated conductivity; the noninteger alpha- solitons are responsible for the depolarization of the FE order. We propose that the (anti) ferroelectricity does exists hiddenly even in the 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.