Transport Property of an Organic Conductorα-(BEDT-TTF)2I3under High Pressure - Discovery of a Novel Type of Conductor -

Tajima, Naoya; Tamura, Masafumi; Nishio, Y.; Kajita, Kôji; Iye, Yasuhiro

doi:10.1143/jpsj.69.543

Cited by 161 publications

(184 citation statements)

References 11 publications

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“…This situation at finite temperature resembles the case of θ-CsZn in which stripe and threefold CO are competing. As shown in Figure 21b, the linewidth of ν 2 3 of α-I 3 decreases by almost half at 0.65 GPa and it becomes comparable to the linewidth of ν 2 3 of α-NH 4 Hg at 100 K. It is known that the application of hydrostatic pressure suppresses the long-range CO state [144]. This result implies that the paramagnetic metal is stabilized more than other stripe COs, and thus the energy difference between them is enlarged under hydrostatic pressure.…”

Section: Fluctuation Of Charge Order In Metallic Phasementioning

confidence: 80%

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: Fluctuation Of Charge Order In Metallic Phasementioning

confidence: 80%

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

Yakushi

2012

Crystals

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“…The Hall coefficient at low temperatures become 10 5 -10 6 times larger than those at room temperature [19,[22][23][24].…”

Section: Introductionmentioning

confidence: 90%

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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“…These anomalous behaviors could be examined by the distinguishable band structure in this salt, for example, the point node structure. The temperature dependence of the carrier density, n, showed T 2 dependence below 100 K from Hall-effect measurement, 16 and this behavior is thought to be related with the decrease in the spin susceptibility in low temperature. In the theoretical study, the disproportionation of the spin fraction between each molecular site is predicted as C Ͼ A Ͼ B and the spin susceptibility vanishes at low temperature.…”

Section: Spin Susceptibility In Zgs Statementioning

confidence: 99%

“…In addition, the strong temperature dependence of the Hall coefficient is reported and the high mobility state in low temperature was predicted. 16 The narrow energy gap electron system was suggested by the band calculation of this salt and the zero-gap-semiconductor ͑ZGS͒ phase in the noninsulating state is proposed. 17 The band structure of the salt has a discriminative feature.…”

mentioning

confidence: 96%

Local spin susceptibility in the zero-gap-semiconductor state ofα−(BEDT-TTF)2I3probed by
Hirose
¹
,
Kawamoto
²

2010
Phys. Rev. B
12
2
15
0
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␣-͑BEDT-TTF͒ 2 I 3 has a double column structure with three crystallographically independent molecules, A, B, and C, and becomes an insulator below 135 K due to a charge-ordering ͑CO͒ transition. The CO state is suppressed under pressure and shows weak temperature dependence of the electrical resistance. The decline of the carrier density is observed over 1.8 GPa, suggesting a zero-gap-semiconductor state under high pressure. The local susceptibility on each site provides important information about the electronic band structure. In our previous work, molecular site B became spin poor and molecular site C became spin rich in the metallic state, suggesting the disproportionation of the local spin density. Therefore, it is worthwhile to investigate the behavior of the electron properties of each molecular site. We accessed the 13 C-NMR in this salt at ambient pressure and at 2.1 GPa. The analysis of the local spin susceptibility suggests that the disproportionation of the spin susceptibility at 2.1 GPa is enhanced from that at ambient pressure, and the spin susceptibility vanishes at low temperature at 2.1 GPa. Moreover, from the temperature dependence of T 1 −1 , we obtain the relation of.

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Transport Property of an Organic Conductorα-(BEDT-TTF)₂I₃under High Pressure - Discovery of a Novel Type of Conductor -

Cited by 161 publications

References 11 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

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

Local spin susceptibility in the zero-gap-semiconductor state ofα−(BEDT-TTF)2I3probed by
Hirose
¹
,
Kawamoto
²

2010
Phys. Rev. B
12
2
15
0
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Transport Property of an Organic Conductorα-(BEDT-TTF)2I3under High Pressure - Discovery of a Novel Type of Conductor -

Cited by 161 publications

References 11 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

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

Local spin susceptibility in the zero-gap-semiconductor state ofα−(BEDT-TTF)2I3probed byHirose1, Kawamoto2 2010Phys. Rev. B122150View full textAdd to dashboardCite

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Transport Property of an Organic Conductorα-(BEDT-TTF)₂I₃under High Pressure - Discovery of a Novel Type of Conductor -

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

Local spin susceptibility in the zero-gap-semiconductor state ofα−(BEDT-TTF)2I3probed by
Hirose
¹
,
Kawamoto
²

2010
Phys. Rev. B
12
2
15
0
View full text Add to dashboard Cite