Phase Competition, Solitons, and Domain Walls in Neutral–Ionic Transition Systems

Tsuchiizu, Masahisa; Yoshioka, Hideo; Seo, Hitoshi

doi:10.7566/jpsj.85.104705

Cited by 17 publications

(31 citation statements)

References 41 publications

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“…2A), indicating that the charge transport is confined in the chains in the crossover region. The NIDW, which separates the neutral and ionic segments, carries a topological charge of ρ NIDW = ± e (ρ I − ρ N )/2 ( 22 ) and is mobile only within the 1D chain, where ρ I and ρ N are the molecular valences in the I and N phases, respectively, and e is the elementary charge. In general, the neutral and ionic segments are 3D-locked by long-range Coulomb interactions.…”

Section: Resultsmentioning

confidence: 99%

“…A decrease in resistivity was reported in two-terminal measurements around this region ( 23 , 25 ). In the present study, we carry out four-terminal resistivity measurements of TTF-CA along three crystal axes under finely tuned pressure to reveal the topological charge transport of the NIDWs and perform 13 C-NMR (nuclear magnetic resonance) measurements to verify the involvement of spin solitons in the topological charge transport, as theoretically suggested ( 21 , 22 , 28 ).…”

Section: Introductionmentioning

confidence: 95%

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Topological charge transport by mobile dielectric-ferroelectric domain walls

et al. 2019

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The concept of topology has been widely applied in condensed matter physics, leading to the identification of peculiar electronic states on three-dimensional (3D) surfaces or 2D lines separating topologically distinctive regions. In the systems explored so far, the topological boundaries are built-in walls; thus, their motional degrees of freedom, which potentially bring about new paradigms, have been experimentally inaccessible. Here, working with a quasi-1D organic material with a charge-transfer instability, we show that mobile neutral-ionic (dielectric-ferroelectric) domain boundaries with topological charges carry strongly 1D-confined and anomalously large electrical conduction with an energy gap much smaller than the one-particle excitation gap. This consequence is further supported by nuclear magnetic resonance detection of spin solitons, which are required for steady current of topological charges. The present observation of topological charge transport may open a new channel for broad charge transport–related phenomena such as thermoelectric effects.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Topological charge transport by mobile dielectric-ferroelectric domain walls

et al. 2019

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“…The present experiments reveal that, in an organic ferroelectric material, TTF-QCl 4 , the former transitions to the latter through the separation of the charge-transfer and lattice instabilities. The separation of the two instabilities possibly generates mobile neutral-ionic domain walls and solitons, which carry electric currents; indeed, recent theoretical studies [26,27] Supplementary Material for the Paper "Separation of Charge Instability and Lattice Symmetry Breaking in an Organic Ferroelectric"…”

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confidence: 99%

Revisited phase diagram on charge instability and lattice symmetry breaking in the organic ferroelectric TTF-QCl4

Takehara¹,

Sunami²,

Iwase³

et al. 2018

Phys. Rev. B

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We investigate the charge and lattice states in a quasi-one-dimensional organic ferroelectric material, TTF-QCl4, under pressures of up to 35 kbar by nuclear quadrupole resonance experiments. The results reveal a global pressure-temperature phase diagram, which spans the electronic and ionic regimes of ferroelectric transitions, which have so far been studied separately, in a single material. The revealed phase diagram clearly shows that the charge-transfer instability and the lattice symmetry breaking, which coincide in the electronic ferroelectric regime at low pressures, bifurcate at a certain pressure, leading to the conventional ferroelectric regime. The present results reveal that the crossover from electronic to ionic ferroelectricity occurs through the separation of charge and lattice instabilities.

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“…Recently, a paraelectric ionic phase with a uniform lattice has been found in the high pressure and high temperature region, 89,90 and it has been poposed that bond-length alternation is destroyed by thermal or quantum fluctuations of soliton pairs in the phase, where a soliton is a topological defect between I A and I B domains. [89][90][91][92] To investigate these mechanisms for polarization reversal, we need to establish an effective model where the THz-pulse induced dynamics can be calculated taking the effects of soliton pairs into account in large systems.…”

Section: Summary and Discussionmentioning

confidence: 99%

Terahertz pulse induced transitions between ionic and neutral phases and electronic polarization reversal in TTF-CA

2019

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We have investigated the terahertz (THz)-pulse induced dynamics of tetrathiafulvalene-pchloranil near the boundary between the ionic and neutral phases with the use of exact numerical calculations of an extended Hubbard model coupled with lattice motion. For the ionic phase, when the applied electric field of the THz-pulse opposes the electronic contribution to the electric polarization (electronic polarization)P el of the ground state and the maximum amplitude of electric field is greater than a threshold value, the THz-pulse excited state changes as I A → N → I B → N → I A → N → • • • (I A ground state case) or I B → N → I A → N → I B → N → • • • (I B ground state case), where N shows the neutral state, I A (I B) shows the ionic state withP el < 0 (P el > 0), and the phase of the bond length alternation of I A is opposite to that of I B. For the neutral phase, when the maximum amplitude of the electric field is greater than a threshold value, the THz-pulse excited state changes as N → I B → N → I A → N → I B → • • • (positive electric field case) or N → I A → N → I B → N → I A → • • • (negative electric field case). The phase transitions and electronic polarization reversal are driven by time variation of the lattice order parameter, which indicates the magnitude and phase of the bond length alternation, and the lattice motion is induced by THz-pulse excitation through the electron-lattice coupling. Transitions between the ionic and neutral phases occur and electronic polarization reverses on a picosecond time scale together with the realizable magnitude of the THz pulse both in the ionic and neutral phases near the phase boundary.

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Phase Competition, Solitons, and Domain Walls in Neutral–Ionic Transition Systems

Cited by 17 publications

References 41 publications

Topological charge transport by mobile dielectric-ferroelectric domain walls

Topological charge transport by mobile dielectric-ferroelectric domain walls

Revisited phase diagram on charge instability and lattice symmetry breaking in the organic ferroelectric TTF-QCl4

Terahertz pulse induced transitions between ionic and neutral phases and electronic polarization reversal in TTF-CA

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