J. Phys. IV France 12 (2002) Pr9-149
DOI: 10.1051/jp4:20020382
Theory of the ferroelectric Mott-Hubbard phase in organic conductors
S. Brazovskii1, 21 Laboratoire de Physique Théorique et des Modèles Statistiques, CNRS, bâtiment 100, Université Paris-Sud, 91405 Orsay, France
2 L.D. Landau Institute for Theoretical Physics, Kosygina Str. 2, 119334 Moscow, Russia
Abstract
Recently the ferroelectric FE anomaly (Nad, Monceau, et al.) followed by the charge
disproportionation CD (Brown, et al) have been discovered in (
TMTTF)2X compounds. A
theory of the combined Mott-Hubbard state describes both effects by interference of the build-in
nonequivalence of bonds and the spontaneous one of sites. The state gives rise to three types of
solitons:
solitons (holons) are observed via the activation energy A in conductivity G; noninteger
solitons provide the frequency dispersion of the FE response; combined spin-charge solitons
determine
G(T) below subsequent phase transitions. The optical edge lies well below the conductivity
gap 2A; the critical FE mode coexists with a combined electron-phonon resonance and a phonon
antiresonance. The CD and the FE can exists hiddenly even in the Se subfamily giving rise to the
unexplained yet low frequency optical peak, the enhanced pseudogap and traces of phonons activation.
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