Charge Order–Disorder Phase Transition in α'-[Bis(ethylenedithio)tetrathiafulvalene]2IBr2 [α'-(BEDT-TTF)2IBr2]

Yue, Yue; Nakano, Chikako; Yamamoto, Kaoru; Uruichi, Mikio; Wojciechowski, R.; Inokuchi, Makoto; Yakushi, Kyuya; Kawamoto, Atsushi

doi:10.1143/jpsj.78.044701

Cited by 21 publications

(18 citation statements)

References 41 publications

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“…This charge fluctuation modulates the frequencies of ν 27 and ν 2 with an amplitude Δ f and correlation time τ. When the site charge fluctuates stochastically between two values such as ρ R and ρ P and thus the frequency fluctuates between ω R and ω P with a transition rate γ, then the line shape of the charge-sensitive mode is described by the following equation [58].…”

Section: The Line Shape Of Charge-sensitive Modementioning

confidence: 99%

“…These two stripes are probably competing and generate frustration in this compound. Yue et al, analyzed the resistivity and magnetic susceptibility [58]. They found that the resistivity curve is approximately expressed by a single exponential curve below ~210 K, whereas it cannot be expressed by a single exponential curve above ~210 K, where the activation energy exponentially decreases against 1/T.…”

Section: Optical Conductivity Of α-(Bedt-ttf) 2 Imentioning

confidence: 99%

“…Therefore, this compound has three phase transitions at ~210 K, ~160 K, and ~30 K. This behaviour is different from that of α-I 3 , in which all of these transitions occur at the same temperature (~135 K). Figure 26 shows the infrared-active ν 27 mode and Raman-active ν 2 and ν 3 modes along with the electrical resistivity [58]. The charge-sensitive ν 27 and ν 2 modes are already split at room temperature, and the spectral change against temperature is continuous as in θ-Cu 2 (CN)[N(CN) 2 ] 2 and θ m -TlZn.…”

Section: Optical Conductivity Of α-(Bedt-ttf) 2 Imentioning

confidence: 99%

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Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Yakushi

2012

Crystals

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This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF) 2 X, and α-(BEDT-TTF) 2 X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy in addition to optical conductivity measurements. It was found that β″-(BEDT-TTF)(TCNQ) changes continuously from a uniform metal to a chargeordered metal with increasing temperature. Although charge disproportionation was clearly observed, long-range charge order is not realized. Among six θ-type salts, four compounds with a narrow band show the metal-insulator transition. However, they maintain a large amplitude of charge order (Δρ~0.6) in both metallic and insulating phases. In the X = CsZn(SCN) 4 salt with intermediate bandwidth, the amplitude of charge order is very small (Δρ < 0.07) over the whole temperature range. However, fluctuation of charge order is indicated in the Raman spectrum and optical conductivity. No indication of the fluctuation of charge order is found in the wide band X = I 3 salt. In α-(BEDT-TTF) 2 I 3 the amplitude of charge order changes discontinuously from small amplitude at high temperature to large amplitude (Δρ max~0 .6) at low temperature. The long-range chargeordered state shows ferroelectric polarization with fast optical response. The fluctuation of multiple stripes occurs in the high-temperature metallic phase. Among α-(BEDT-TTF) 2 MHg(SCN) 4 (X = NH 4 , K, Rb, Tl), the fluctuation of charge order is indicated only in the X = NH 4 salt. α′-(BEDT-TTF) 2 IBr 2 shows successive phase transitions to the ferroelectric state keeping a large amplitude of charge order (Δρ max~0 .8) over the whole temperature range. It was found that the amplitude and fluctuation of charge order in these compounds is enhanced as the kinetic energy (bandwidth) decreases. OPEN ACCESSCrystals 2012, 2 1292

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Section: The Line Shape Of Charge-sensitive Modementioning

confidence: 99%

Section: Optical Conductivity Of α-(Bedt-ttf) 2 Imentioning

confidence: 99%

Section: Optical Conductivity Of α-(Bedt-ttf) 2 Imentioning

confidence: 99%

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Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Yakushi

2012

Crystals

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“…22 However the charge disproportionation has been observed above 200 K and there is not any qualitative changes at around 200 K where the conductivity showed the anomaly. Moreover, it was also suggested that by applying pressures, the charge disproportionation of this salt vanished and the anomaly observed at ambient pressure changed to metal-insulator ͑MI͒ transition with hysteresis.…”

Section: Introductionmentioning

confidence: 95%

“…Moreover, it was also suggested that by applying pressures, the charge disproportionation of this salt vanished and the anomaly observed at ambient pressure changed to metal-insulator ͑MI͒ transition with hysteresis. 22 It is important to reveal the nature of the anomaly and to clarify whether the anomaly is a phase transition or not. If the anomaly is a phase transition, this salt gives valuable information about the connection between CO transition at ambient pressure and the conventional MI transition without the charge disproportionation under pressures and the different type of CO transition from those in ␣ and modifications.…”

Section: Introductionmentioning

confidence: 99%

C13NMR study on the charge-ordering saltα′−(

Hirose

Kawamoto

2009

Phys. Rev. B

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Among quasi-two-dimensional organic conductors, ͑BEDT-TTF͒ 2 X, what form the two column structure of ␣ or is thought to show a charge-ordering insulating state. The ␣Ј modification is the other candidate for a charge-ordering state. To determine the existence of a charge-ordering state and electron magnetism in the ␣Ј phase, which has a symmetry that differs from that of the ␣ and phases, we utilized 13 C-NMR to examine ␣Ј-͑BEDT-TTF͒ 2 IBr 2 in which one side of the central carbon on the BEDT-TTF molecule is substituted with 13 C nuclei. We observed changes in its spectrum at 200 K. The angular dependence of the NMR shift at 15 K indicated that the charge-ordering pattern is intracolumn disproportionation and the ratio of charge disproportionation on the spin-poor site and spin-rich sites is almost 1:0. The angle dependence of NMR spectrum at 60 K suggests that the hyperfine coupling tensor in the paramagnetic charge-ordering state is determined not only by the charge density of on-site molecules but also by the contribution of off-site molecules. The change in hyperfine coupling tensor must be taken into account in NMR studies of the paramagnetic CO state.

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Spectroscopic characterization of charge order fluctuations in BEDT‐TTF metals and superconductors

Girlando

Masino

Kaiser

et al. 2012

Physica Status Solidi (b)

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The charge-fluctuating and charge-ordered states in metallic, insulating and superconducting bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) salts are characterized through the analysis of the infrared (IR) spectral region relevant to the C --C antisymmetric stretch, b 1 n 22 . This spectral region shows dramatic changes in band intensity and band-shape by varying the temperature. The observed spectral features can be understood on the basis of an extension of the well-known Kubo model for the spectral signatures of an equilibrium between two states. The two-orders of magnitude increase in the IR oscillator strength of the b 1 n 22 mode upon ionization has also to be taken into account.BEDT-TTF C --C antisymmetric stretch, b 1 n 22 .

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Charge Order–Disorder Phase Transition in α'-[Bis(ethylenedithio)tetrathiafulvalene]₂IBr₂ [α'-(BEDT-TTF)₂IBr₂]

Cited by 21 publications

References 41 publications

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

C13NMR study on the charge-ordering saltα′−(

Spectroscopic characterization of charge order fluctuations in BEDT‐TTF metals and superconductors

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