Strong Optical Nonlinearity and its Ultrafast Response Associated with Electron Ferroelectricity in an Organic Conductor

Yamamoto, Kaoru; Iwai, Shinichiro; Boyko, Sergiy; Kashiwazaki, Akimitsu; Hiramatsu, F.; Okabe, Chie; Nishi, Nobuyuki; Yakushi, Kyuya

doi:10.1143/jpsj.77.074709

Cited by 150 publications

(179 citation statements)

References 32 publications

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“…An x-ray diffraction study supported P1, and showed a horizontal stripe structure [128]. Decisive evidence for the breaking of inversion symmetry was given by the experiment of second harmonic generation (SHG) [124]. Recently, Alemany et al, pointed out that the hydrogen bond between the ethylene groups of BEDT-TTF and I 3 − plays an essential role in the CO transition of α-I 3 [129].…”

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

confidence: 99%

“…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%

“…All of these results studied by vibrational spectroscopy, x-ray diffraction, and 13 C-NMR approximately consistent with each other. Yamamoto et al, found strong second harmonic generation (SHG) in the CO state, using 4 ps pulse laser with a wavelength of 1.4 µm as the fundamental light [124,136]. The evolution of the second harmonic light just below T CO is direct evidence for the breakdown of the inversion symmetry.…”

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

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

confidence: 99%

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

confidence: 99%

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

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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“…8 Indeed, a CO state was confirmed in ␣-͑BEDT-TTF͒ 2 I 3 and -͑BEDT-TTF͒ 2 RbZn͑SCN͒ 4 and in similar salts. [9][10][11][12][13][14] Moreover, superconductivity was observed in ␣-͑BEDT-TTF͒ 2 I 3 under uniaxial stress and in -͑BEDT-TTF͒ 2 I 3 ͑Refs. 15 and 16͒ under ambient pressure.…”

Section: Introductionmentioning

confidence: 94%

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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“…Yamamoto et al applied this method to α-ET 2 I 3 discussed in the previous subsection, and found a clear SHG signal below the charge order transition at 135 K [108,109]. They also detected a novel series of dielectric phases in α -ET 2 IBr 2 [110]; below T 200K, the inter-layer antiferroelectric phase appears (without the SHG signal), and it turns into a ferroeletric phase at T < 160 K, where the SHG signal sets in.…”

Section: Spin Liquids Dielectricsmentioning

confidence: 99%

Theories on Frustrated Electrons in Two-Dimensional Organic Solids

Hotta

2012

Crystals

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Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to many interesting states of matter in the two insulators and in the metals adjacent to them. This review is concerned with the theoretical studies on such issue over the past ten years, and provides the systematic understanding on exotic metals, dielectrics, and spin liquids, which are the consequences of the competing correlation and fluctuation under frustration.

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Strong Optical Nonlinearity and its Ultrafast Response Associated with Electron Ferroelectricity in an Organic Conductor

Cited by 150 publications

References 32 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′−(

Theories on Frustrated Electrons in Two-Dimensional Organic Solids

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