Physics of Neutral-to-Ionic Phase Transition in Organic Charge Transfer Semiconducting Compounds

• Authors: H. Cailleau , M.H. Lemée-Cailleau , M. Le Cointe , T. Luty
• Languages of publication: EN

Abstracts

EN

An uncommon excitonic instability takes place in some exotic semiconducting compounds. Indeed, the equilibrium neutral-to-ionic (N-I) phase transition, as well as the non-equilibrium photo-induced phase transformation, observed in some organic charge-transfer complexes, originate from intra- and inter-chain cooperative effects between structurally relaxed charge-transfer excitations. This electronic-structural phase transition manifests itself by a change of the degree of charge-transfer and a dimerization distortion with the formation of donor-acceptor pairs along the stacking axis in the I phase. Thermal charge-transfer excitations associated with the formation of I strings along N chains are at the heart of the mechanism of this phase transition. These relaxed electronic excitations, which are an intrinsic feature of low-dimensional systems with strong electron-phonon coupling, can be described in terms of self-trapping and self-multiplication of charge-transfer excitons. Precise structural studies on the prototype compound, tetrathiafulvalene-p-chloranil allow to highlight the respective role taken by the ionicity and the dimerization. Symmetry and thermodynamics analysis of the N-I transition, based on recent determination of the pressure-temperature phase diagram, make possible to present a consistent picture of this phase transition. Supported by theoretical considerations taking into account the interplay between quantum and thermal effects, the experimental observations show that the N-I transition results from the condensation and the ordering (crystallization) of charge-transfer excitations, following a phase diagram analogous to the solid-liquid-gas one.

Keywords

EN

71.38.+i; 61.50.Ks; 71.35.Aa

• Publisher: Institute of Physics, Polish Academy of Sciences
• Journal: Acta Physica Polonica A
• Year: 1997
• Volume: 92
• Issue: 4
• Pages: 597-608

Dates

published

1997-10

Contributors

author

H. Cailleau

• Groupe Matière Condensée et Matériaux, UMR CNRS 6626, Université de Rennes 1, 35042 Rennes cedex, France

author

M.H. Lemée-Cailleau

• Groupe Matière Condensée et Matériaux, UMR CNRS 6626, Université de Rennes 1, 35042 Rennes cedex, France

author

M. Le Cointe

• Groupe Matière Condensée et Matériaux, UMR CNRS 6626, Université de Rennes 1, 35042 Rennes cedex, France

author

T. Luty

• Institute of Physical and Theoretical Chemistry, Technical University of Wrocław, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland