Summary for Theory of the Ferroelectric Phase in Organic Conductors in Relation to Experiments

TL;DR

This paper reviews the discovery and explanation of ferroelectricity and charge disproportionation in (TMTTF)2X organic conductors, unifying various phenomena like structural instability, solitons, and electronic symmetries, with implications for experimental observations.

Contribution

It provides a theoretical framework linking ferroelectricity, charge disproportionation, and solitons in organic conductors, clarifying their experimental signatures and underlying physics.

Findings

Identification of ferroelectricity as the cause of high-temperature transitions

Observation of solitons carrying fractional charge and spin

Connection between structural and electronic symmetries

Abstract

Mysterious high temperature structureless transitions in (TMTTF)2X compounds have been discovered in mid 80's (Coulon, Lawersanne,vet al), but left unexplained and abandoned, together with other warnings from structural effects (Moret, Pouget, et al), with dramatic consequences for the whole field. Recently their nature has been identified as the ferroelectricity (Nad, Monceau, et al) and, more generally, the charge disproportionation (Brown, et al). New phenomena unify an unusual variety of concepts: ferroelectricity of good conductors, structural instability towards Mott- Hubbard state, Wigner crystallization in a dense electronic system, ordered 4kF density wave, richness of physics of solitons, interplay of structural and electronic symmetries. The ferroelectric state gives rise to several types of solitons carrying electronic charge, a noninteger charge, spin or both spin and charge in special cases. They are clearly observed via conductivity, electric and magnetic susceptibilities. Solitons are challenging for optics where they already seem to determine the pseudogap in absorption. Various features also appear, or are expected, from collective electronic and coupled electron-phonon modes. REFERENCES: cond-mat/0012237 cond-mat/0304076 cond-mat/0304483 cond-mat/0306006