Chlorine-nuclear-quadrupole-resonance study of the neutral-to-ionic transition in tetrathiafulvalene-chloranil

Gallier, J.; Toudic, Bertrand; Délugeard, Y.; Cailleau, H.; Gourdji, M.; Péneau, A.; Guibé, L.

doi:10.1103/physrevb.47.11688

Cited by 25 publications

(15 citation statements)

References 44 publications

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“…In addition, an anomalous dielectric response associated with a very slow dynamics has been observed and explained in terms of N-I domain walls. However, this interpretation is contradictory with the non-observation of the coexistence of N and I lines in the NQR spectra [14]. The possibility of electric conductivity or random-field (defects, impurities) effects cannot be excluded.…”

Section: Cooperativity and Ct Excitationsmentioning

confidence: 45%

“…We suggest that this is at the origin of the observed large dielectric response along the stack [33]: the divergent increase, on approaching TN-1, almost independent of frequency, is too large to be attributed to the softening of the polar dimerization mode. In the same way, spin-lattice relaxation rates Τ 1 in NQR measurements [14] reveal the existence of pretransitional fluctuations with a predominant one-dimensional character. In addition, an anomalous dielectric response associated with a very slow dynamics has been observed and explained in terms of N-I domain walls.…”

Section: Cooperativity and Ct Excitationsmentioning

confidence: 89%

“…The changes in geometry of CA molecule are closely correlated with 35Cl nuclear quadrupole resonance (NQR) results [14]: the ionicity change leads to a large frequency shift between lines of N and I phases, while the dimerization induces a splitting of the I lines. Since the frequency shift for each chlorine nucleus is proportional in a first approximation to the local distortion, this splitting is proportional to n. The lifetime of transient structurally relaxed CT excitations in the N phase, as measured by photoinduced experiments, is in the nanosecond range [9].…”

Section: Symmetry Analysis and Electronic-structural Changesmentioning

confidence: 99%

“…Rather small concentration of thermal CT excitations makes the transition discontinuous with no indication of a large disordered state in the N phase. Actually, only weak precursor effectS are indicated in the behavior of NQR frequencies [14], while a small-softening of low-frequency polar lattice-mode is observed by far-infrared spectroscopy [29]. Pressure not only favors the I phase (increase in Madelung energy) [30] but also strongly stimulates quantum mixing (increase in transfer integral [31]) which changes the ground states and makes N and I "compounds" more and more similar.…”

Section: Cooperativity and Ct Excitationsmentioning

confidence: 99%

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

Cailleau¹,

Lemée-Cailleau²,

Cointe³

et al. 1997

Acta Phys. Pol. A

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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 pole 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.

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Section: Cooperativity and Ct Excitationsmentioning

confidence: 45%

Section: Cooperativity and Ct Excitationsmentioning

confidence: 89%

Section: Symmetry Analysis and Electronic-structural Changesmentioning

confidence: 99%

Section: Cooperativity and Ct Excitationsmentioning

confidence: 99%

See 2 more Smart Citations

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

Cailleau¹,

Lemée-Cailleau²,

Cointe³

et al. 1997

Acta Phys. Pol. A

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“…Beside the intramolecular vibrational probes already mentioned, 35 Cl Nuclear Quadrupolar Resonance (NQR) provides exceptionally sensitive local probes of CA (C 6 Cl 4 O 2 ) molecular changes. This allows following the evolution of both symmetry breaking and totally symmetrical changes with temperature ( Figure 4) [24][25][26], as well as under pressure [8].…”

Section: Symmetry Analysis and Structural Changes Of Ttf-camentioning

confidence: 99%

Back to the Structural and Dynamical Properties of Neutral-Ionic Phase Transitions

et al. 2017

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Abstract:Although the Neutral-Ionic transition in mixed stack charge-transfer crystals was discovered almost forty years ago, many features of this intriguing phase transition, as well as open questions, remain at the heart of today's science. First of all, there is the most spectacular manifestation of electronic ferroelectricity, in connection with a high degree of covalency between alternating donor and acceptor molecules along stacks. In addition, a charge-transfer instability from a quasi-neutral to a quasi-ionic state takes place concomitantly with the stack dimerization, which breaks the inversion symmetry. Moreover, these systems exhibit exceptional one-dimensional fluctuations, with an enhancement of the effects of electron-lattice interaction. This may lead to original physical pictures for the dynamics of pre-transitional phenomena, as the possibility of a pronounced Peierls-type instability and/or the generation of unconventional non-linear excitations along stacks. Last but not least, these mixed stack charge-transfer systems constitute a valuable test bed to explore some of the key questions of ultrafast photo-induced phenomena, such as multiscale dynamics, selective coherent excitations and non-linear responsiveness. These different aspects will be discussed through the structural and dynamical features of the neutral-ionic transition, considering old and recent results, open questions and future opportunities. In particular, we revisit the structural changes and symmetry considerations, the pressure-temperature phase diagrams and conclude by their interplay with the photo-induced dynamics.

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NQRS Data for C12H4Cl4O2S4 [C6Cl4O2·C6H4S4] (Subst. No. 1322)

Chihara¹,

Nakamura²

2010

Substances Containing C10H16 … Zn

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Chlorine-nuclear-quadrupole-resonance study of the neutral-to-ionic transition in tetrathiafulvalene-chloranil

Cited by 25 publications

References 44 publications

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

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

Back to the Structural and Dynamical Properties of Neutral-Ionic Phase Transitions

NQRS Data for C12H4Cl4O2S4 [C6Cl4O2·C6H4S4] (Subst. No. 1322)

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