Charge disproportionation in the organic conductor, α-(BEDT-TTF)2I3

Takano, Yoshiki; Hiraki, K.; Yamamoto, Hiroshi; Nakamura, Toshikazu; Takahashi, Toshihiro

doi:10.1016/s0022-3697(00)00173-6

Cited by 148 publications

(111 citation statements)

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“…The exact site assignment is not settled yet, since these values differ slightly from those found in the NMR, vibrational infrared and Raman spectroscopy, and anomalous x-ray diffraction measurements. [25][26][27][28][29][30] Nevertheless, all these experiments consistently indicate that the charge order comprises "horizontal" charge stripes of charge-poor (CP) sites, the A ′ and C molecules, and charge-rich (CR) sites (A and B molecules) along the b crystallographic axis, as depicted in Fig. 1(b).…”

Section: Molecules (Bedt-ttfmentioning

confidence: 65%

“…24,26 . As demonstrated by nuclear magnetic resonance (NMR) 25 and synchrotron x-ray diffraction measurements, 26 charge order at long length scales develops fully below the metal-toinsulator phase transition T CO = 136 K. At T CO the conductivity drops by several orders of magnitude and a temperature-dependent gap opens in charge and spin sector which indicates insulating and diamagnetic nature of the ground state. x-ray diffraction measurements indicate subtle structural changes at T CO .…”

Section: Molecules (Bedt-ttfmentioning

confidence: 99%

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Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I
Ivek
¹
,
Korin-Hamzić
²
,
Milat
³

et al. 2011
Phys. Rev. B
83
20
150
2
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We report on the anisotropic response, the charge and lattice dynamics of normal and chargeordered phases with horizontal stripes in single crystals of the organic conductor α-(BEDT-TTF)2I3 determined by dc resistivity, dielectric and optical spectroscopy. An overdamped Drude response and a small conductivity anisotropy observed in optics is consistent with a weakly temperature dependent dc conductivity and anisotropy at high temperatures. The splitting of the molecular vibrations ν27(Bu) evidences the abrupt onset of static charge order below TCO = 136 K. The drop of optical conductivity measured within the ab plane of the crystal is characterized by an isotropic gap that opens of approximately 75 meV with several phonons becoming pronounced below. Conversely, the dc conductivity anisotropy rises steeply, attaining at 50 K a value 25 times larger than at high temperatures. The dielectric response within this plane reveals two broad relaxation modes of strength ∆εLD ≈ 5000 and ∆εSD ≈ 400, centered at 1 kHz < νLD < 100 MHz and νSD ≈ 1 MHz. The anisotropy of the large-mode (LD) mean relaxation time closely follows the temperature behavior of the respective dc conductivity ratio. We argue that this phason-like excitation is best described as a long-wavelength excitation of a 2kF bond-charge density wave expected theoretically for layered quarter-filled electronic systems with horizontal stripes. Conversely, based on the theoretically expected ferroelectric-like nature of the charge-ordered phase, we associate the small-mode (SD) relaxation with the motion of domain-wall pairs, created at the interface between two types of domains, along the a and b axes. We also consider other possible theoretical interpretations and discuss their limitations.

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Section: Molecules (Bedt-ttfmentioning

confidence: 65%

Section: Molecules (Bedt-ttfmentioning

confidence: 99%

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I
Ivek
¹
,
Korin-Hamzić
²
,
Milat
³

et al. 2011
Phys. Rev. B
83
20
150
2
View full text Add to dashboard Cite

show abstract

“…In the case of a two-dimensional organic compound, Moldenhauer et al, reported that localization of charge occurs in one of the stacks of α-(BEDT-TTF) 2 I 3 (BEDT-TTF corresponds to bis(ethylenedithio) tetrathiafulvalene) [12]. After the theoretical prediction of the CO ground state for α-(BEDT-TTF) 2 I 3 by Kino and Fukuyama [13], CO in two-dimensional organic compounds was suggested in α-(BEDT-TTF) 2 I 3 [14], and more clearly shown in θ-(BEDT-TTF) 2 RbZn(SCN) 4 [15]. Stimulated by the experimental findings of CO, theoretical studies were conducted on the role of intersite Coulomb interaction in CO [16][17][18], lattice distortion accompanied by CO [19][20][21], the relationship between CO fluctuation and superconductivity (SC) [22], and quantum criticality at the edge of CO [23].…”

Section: Introductionmentioning

confidence: 99%

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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“…The origin of the insulator phase has been studied theoretically using the mean field approximation [6][7][8][9], and the stripe charge ordering was proposed by introducing the extended Hubbard model with the on-site and nearest-neighbor Coulomb interaction [7]. From the nuclear magnetic resonance (NMR) experiments [10] and the angular dependence of 13 C-NMR line shape, it was confirmed that the charge stripes run along the direction perpendicular to the a-axis [11]. The charge disproportionation that exists even above T MI develops as temperature decreases from room temperature to T MI [12].…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of the zero-gap organic conductor α-(BEDT-TTF)₂I₃

Kobayashi

Katayama

Suzumura

2009

Science and Technology of Advanced Materials

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The quasi-two-dimensional molecular conductor α-(BEDT-TTF) 2 I 3 exhibits anomalous transport phenomena where the temperature dependence of resistivity is weak but the ratio of the Hall coefficient at 10 K to that at room temperature is of the order of 10 4 . These puzzling phenomena were solved by predicting massless Dirac fermions, whose motions are described using the tilted Weyl equation with anisotropic velocity. α-(BEDT-TTF) 2 I 3 is a unique material among several materials with Dirac fermions, i.e. graphene, bismuth, and quantum wells such as HgTe, from the view-points of both the structure and electronic states described as follows. α-(BEDT-TTF) 2 I 3 has the layered structure with highly two-dimensional massless Dirac fermions. The anisotropic velocity and incommensurate momenta of the contact points, ±k 0 , originate from the inequivalency of the BEDT-TTF sites in the unit cell, where ±k 0 moves in the first Brillouin zone with increasing pressure. The massless Dirac fermions exist in the presence of the charge disproportionation and are robust against the increase in pressure. The electron densities on those inequivalent BEDT-TTF sites exhibit anomalous momentum distributions, reflecting the angular dependences of the wave functions around the contact points. Those unique electronic properties affect the spatial oscillations of the electron densities in the vicinity of an impurity. A marked behavior of the Hall coefficient, where the sign of the Hall coefficient reverses sharply but continuously at low temperatures around 5 K, is investigated by treating the interband effects of the magnetic field exactly. It is shown that such behavior is possible by assuming the existence of the extremely small amount of electron doping. The enhancement of the orbital diamagnetism is also expected. The results of the present research shed light on a new aspect of Dirac fermion physics, i.e. the emergence of unique electronic properties owing to the structure of the material.

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Charge disproportionation in the organic conductor, α-(BEDT-TTF)2I3

Cited by 148 publications

References 8 publications

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I
Ivek
¹
,
Korin-Hamzić
²
,
Milat
³

et al. 2011
Phys. Rev. B
83
20
150
2
View full text Add to dashboard Cite

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I
Ivek
¹
,
Korin-Hamzić
²
,
Milat
³

et al. 2011
Phys. Rev. B
83
20
150
2
View full text Add to dashboard Cite

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

Theoretical study of the zero-gap organic conductor α-(BEDT-TTF)₂I₃

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Charge disproportionation in the organic conductor, α-(BEDT-TTF)2I3

Cited by 148 publications

References 8 publications

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2IIvek1, Korin-Hamzić2, Milat3 et al. 2011Phys. Rev. B83201502View full textAdd to dashboardCite

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2IIvek1, Korin-Hamzić2, Milat3 et al. 2011Phys. Rev. B83201502View full textAdd to dashboardCite

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

Theoretical study of the zero-gap organic conductor α-(BEDT-TTF)2I3

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Product

Resources

About

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I
Ivek
¹
,
Korin-Hamzić
²
,
Milat
³

et al. 2011
Phys. Rev. B
83
20
150
2
View full text Add to dashboard Cite

Electrodynamic response of the charge ordering phase: Dielectric and optical studies ofα-(BEDT-TTF)2I
Ivek
¹
,
Korin-Hamzić
²
,
Milat
³

et al. 2011
Phys. Rev. B
83
20
150
2
View full text Add to dashboard Cite

Theoretical study of the zero-gap organic conductor α-(BEDT-TTF)₂I₃