Effects of Uniaxial Strain on Transport Properties of Organic Conductor   α-(BEDT-TTF)<sub>2</sub>I<sub>3</sub> and Discovery of Superconductivity

Tajima, Naoya; Ebina-Tajima, Akiko; Tamura, Masafumi; Nishio, Y.; Kajita, Kôji

doi:10.1143/jpsj.71.1832

Cited by 130 publications

(131 citation statements)

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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: 89%

“…By adopting an experimental technique of uniaxial strain [18], it was observed that the superconductivity with the critical temperature T c ∼ 7 K emerges under the pressure (∼ 2 kbar) along the a-axis [19]. The mechanism of such superconductivity was investigated using the extended Hubbard model [20].…”

Section: Introductionmentioning

confidence: 99%

“…Then it was called narrow-gap semiconductor, because it has the properties of both a metal and a semiconductor [19]. The band structure has been examined using the extended Hückel molecular orbital calculation based on the structure analysis by x-ray diffraction.…”

Section: Introductionmentioning

confidence: 99%

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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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“…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: 89%

Section: Introductionmentioning

confidence: 99%

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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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“…Among the various known organic conductors [115][116][117][118], α-(BEDT-TTF) 2 I 3 (abbreviated as α-I 3 ) shows rich electronic properties such as charge ordering [119], superconductivity [120], zero-gap state (ZGS) [121,122], photo-induced phase transition [123], and nonlinear optical response [124].The crystal structure of α-I 3 consists of alternating layers of the anion and donor [125]. The donor layer has a herringbone arrangement of BEDT-TTF molecules.…”

Section: α-(Bedt-ttf) 2 I 3 and Related Compoundsmentioning

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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“…However, graphene is not a bulk crystal but a single layer of graphite. The bulk crystal zero-gap system was realized in the organic conductor α-(BEDT-TTF) 2 I 3 under high pressure [3,4,5,6,7,8]. The existence of the massless Dirac fermions state in bulk crystal has already been discovered in graphite [9,10] and Cd 1−x Hg x Te [11].…”

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confidence: 99%

Effect of the Zero-Mode Landau Level on Interlayer Magnetoresistance in Multilayer Massless Dirac Fermion Systems

et al. 2009

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We report on the experimental results of interlayer magnetoresistance in multilayer massless Dirac fermion system α-(BEDT-TTF)2I3 under hydrostatic pressure and its interpretation. We succeeded in detecting the zero-mode Landau level (n=0 Landau level) that is epected to appear at the contact points of Dirac cones in the magnetic field normal to the two-dimensional plane. The characteristic feature of zero-mode Landau carriers including the Zeeman effect is clearly seen in the interlayer magnetoresistance.

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Effects of Uniaxial Strain on Transport Properties of Organic Conductor α-(BEDT-TTF)₂I₃ and Discovery of Superconductivity

Cited by 130 publications

References 12 publications

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

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

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

Effect of the Zero-Mode Landau Level on Interlayer Magnetoresistance in Multilayer Massless Dirac Fermion Systems

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Effects of Uniaxial Strain on Transport Properties of Organic Conductor α-(BEDT-TTF)2I3 and Discovery of Superconductivity

Cited by 130 publications

References 12 publications

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

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

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

Effect of the Zero-Mode Landau Level on Interlayer Magnetoresistance in Multilayer Massless Dirac Fermion Systems

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Effects of Uniaxial Strain on Transport Properties of Organic Conductor α-(BEDT-TTF)₂I₃ and Discovery of Superconductivity

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

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