Electrical and Structural Properties of θ-type BEDT-TTF Organic Conductors under Uniaxial Strain

Kondo, Ryusuke; Higa, Momoka; Kagoshima, S.; Hoshino, Hirotada; Mori, Toshiyuki; Mori, H.

doi:10.1143/jpsj.75.044716

Cited by 29 publications

(30 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The resemblance between the two figures suggests a relationship between the horizontal stripe and the a-axis threefold correlations. This may also be consistent with an experimental analysis under uniaxial pressure, which concluded that the value of t c is the key factor that dominates the occurrence of horizontal charge ordering [41]. A possible relation between the a-axis threefold and the horizontal stripe orderings will be mentioned in the next subsection.…”

Section: A-axis Threefold Charge Correlationsupporting

confidence: 86%

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

Kuroki

2009

Science and Technology of Advanced Materials

View full text Add to dashboard Cite

A review is given on the theoretical studies of charge correlations in θ-(BEDT-TTF) 2 X . Various studies show that within a purely electronic model on the θ-type lattice with on-site U and nearest neighbor V p and V c interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime V p < V c , V p ∼ V c , and V p > V c , respectively. In the realistic parameter regime of V p ∼ V c , there is competition between the c-axis three fold state and diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron-lattice coupling, which tends to distort the lattice into the θ d -type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron-electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in θ-(BEDT-TTF) 2 X may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed.

show abstract

Section: A-axis Threefold Charge Correlationsupporting

confidence: 86%

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

Kuroki

2009

Science and Technology of Advanced Materials

View full text Add to dashboard Cite

show abstract

“…35 On the other hand, according to the structural analysis of -͑ET͒CsZn͑SCN͒ 4 under uniaxial strain, the uniaxial strain along the transverse direction does not reduce the dihedral angle but reduces the lattice constant along the transverse direction. 39 This result suggests that the overlap integrals are weakly increased under the T-axis strain. Moreover, the averaged dihedral angle of the ET salt is ϳ140°, which is significantly larger than those of the -type ET compounds.…”

Section: Site-charge Distributions Under Uniaxial Strainmentioning

confidence: 92%

“…Kondo et al studied the temperature dependence of the electrical resistance under uniaxial strain. 39 The metallic behavior is preserved in the lowpressure region under the uniaxial strain along the transverse direction ͑corresponding to the a axis͒, but the electrical resistance increases above ϳ10 kbar. 39 This behavior is in agreement with that of the BETS salt under the T-axis strain.…”

Section: Site-charge Distributions Under Uniaxial Strainmentioning

confidence: 98%

“…39 The metallic behavior is preserved in the lowpressure region under the uniaxial strain along the transverse direction ͑corresponding to the a axis͒, but the electrical resistance increases above ϳ10 kbar. 39 This behavior is in agreement with that of the BETS salt under the T-axis strain. However, there is no comment on the nonmetallic state above ϳ10 kbar in the previous report.…”

Section: Site-charge Distributions Under Uniaxial Strainmentioning

confidence: 98%

See 1 more Smart Citation

Charge ordered state and frustration of site charges in(ET)5Te2I6and<

et al. 2007

View full text Add to dashboard Cite

We have carried out x-ray structural analysis and have studied the temperature dependence of vibrational spectra and electrical resistivity under uniaxial strain for ͑ET͒ 5 Te 2 I 6 and ͑BETS͒ 5 Te 2 I 6 ͓ET= bis͑ethylenedithio͒tetrathiafulvalene and BETS= bis͑ethylenedithio͒tetraselenafulvalene͔. In the lowtemperature insulating phase for each salt, a charge-sensitive mode 2 exhibits peak splitting, and a vibronic 3 mode shows factor group splitting. This observation confirms the charge ordered state. The distribution of site charges is determined from the factor group analysis of the vibronic 3 mode, which is in agreement with that determined from x-ray structural analysis of the ET salt. In the high-temperature conducting phase, the vibronic 3 mode is smeared out whereas the frequencies of the two charge-sensitive modes are almost unchanged over the whole temperature range. We have proposed a model wherein the highly conducting state is ascribed to the frustration between the site-charge distributions in the insulating state and the other distribution, which contributes to a reduction in the intersite Coulomb interaction along the stacking and diagonal directions, respectively. Our conjecture is supported by the temperature dependence of the electrical resistivity under the uniaxial strain.

show abstract

“…The electronic phase diagram of this family has been composed employing the dihedral angle φ between the adjacent BEDT-TTF molecules (See Figure 9), which is related to the bandwidth [74]. The dihedral angle was subsequently linked to t c /t p to explain the phase diagram, where t c and t p are the transfer integrals along the c (stacking) direction and a ± c (diagonal) directions forming a triangular lattice [75][76][77][78]. Watanabe discussed this phase diagram using t c /t p as follows [78].…”

Section: θ-(Bedt-ttf) 2 Xmentioning

confidence: 99%

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

Yakushi

2012

Crystals

View full text Add to dashboard Cite

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

show abstract

Electrical and Structural Properties of θ-type BEDT-TTF Organic Conductors under Uniaxial Strain

Cited by 29 publications

References 34 publications

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

Charge ordered state and frustration of site charges in(ET)5Te2I6and<

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

Contact Info

Product

Resources

About

Electrical and Structural Properties of θ-type BEDT-TTF Organic Conductors under Uniaxial Strain

Cited by 29 publications

References 34 publications

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X

Charge ordered state and frustration of site charges in(ET)5Te2I6and<

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

Contact Info

Product

Resources

About

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X

Theoretical aspects of charge correlations in θ-(BEDT-TTF)₂X