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Visentini, G.; Masino, Matteo; Bellitto, Carlo; Girlando, Alberto

doi:10.1103/physrevb.58.9460

Cited by 47 publications

(50 citation statements)

References 32 publications

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“…56,57 The resulting U Ӎ 400 meV is comparable to that deduced from measurements of the frequency-dependent optical conductivity of similar materials. 12,58 This value of U is smaller than values deduced from quantum chemistry calculations on isolated dimers, which do not take into account screening. 59 Using the above values of t and U gives J ϳ 100 K.…”

Section: Comparison With Experimental Systemsmentioning

confidence: 81%

Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants

et al. 2005

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We present the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular lattices, using high-temperature series expansions. We consider a model with two exchange constants J 1 and J 2 on a lattice that interpolates between the limits of a square lattice ͑J 1 =0͒, a triangular lattice ͑J 2 = J 1 ͒, and decoupled linear chains ͑J 2 =0͒. In all cases, the susceptibility, which has a Curie-Weiss behavior at high temperatures, rolls over and begins to decrease below a peak temperature T p . Scaling the exchange constants to get the same peak temperature shows that the susceptibilities for the square lattice and linear chain limits have similar magnitudes near the peak. Maximum deviation arises near the triangular-lattice limit, where frustration leads to much smaller susceptibility and with a flatter temperature dependence. We compare our results to the inorganic materials Cs 2 CuCl 4 and Cs 2 CuBr 4 and to a number of organic molecular crystals. We find that the former ͑Cs 2 CuCl 4 and Cs 2 CuBr 4 ͒ are weakly frustrated and their exchange parameters determined through the temperature dependence of the susceptibility are in agreement with neutron-scattering measurements. In contrast, the organic materials considered are strongly frustrated with exchange parameters near the isotropic triangular-lattice limit.

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Section: Comparison With Experimental Systemsmentioning

confidence: 81%

Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants

et al. 2005

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“…Thus the overall e-lph coupling strength is of the same order of magnitude as that due to e-mv coupling, about 70 meV. 15 We can make a more direct connection with superconducting properties by calculating the Eliashberg function and the dimensionless electron-phonon coupling constant λ. As seen in eq.…”

Section: Electron-phonon Couplingmentioning

confidence: 99%

Lattice dynamics and electron-phonon coupling in theβ−(BEDT−TTF)2I3
Girlando
¹
,
Masino
²
,
Visentini
³

et al. 2000
Phys. Rev. B
35
1
38
0
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The crystal structure and lattice phonons of (BEDT-TTF)2I3 superconducting β-phase (where BEDT-TTF is bis-ethylen-dithio-tetrathiafulvalene) are computed and analyzed by the Quasi Harmonic Lattice Dynamics (QHLD) method. The empirical atom-atom potential is that successfully employed for neutral BEDT-TTF and for non superconducting α-(BEDT-TTF)2I3. Whereas the crystal structure and its temperature and pressure dependence are properly reproduced within a rigid molecule approximation, this has to be removed account for the specific heat data. Such a mixing between lattice and low-frequency intra-molecular vibrations also yields good agreement with the observed Raman and infrared frequencies. From the eigenvectors of the low-frequency phonons we calculate the electron-phonon coupling constants due to the modulation of charge transfer (hopping) integrals. The charge transfer integrals are evaluated by the extended Hückel method applied to all nearest-neighbor BEDT-TTF pairs in the ab crystal plane. From the averaged electron-phonon coupling constants and the QHLD phonon density of states we derive the Eliashberg coupling function α(ω)F (ω), which compares well with that experimentally obtained from point contact spectroscopy. The corresponding dimensionless coupling constant λ is found to be ∼ 0.4. 74.70. Kn,74.25.Kc

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“…[43,53]. The coupling constants of ν 2 and ν 3 were respectively estimated to be g 2 = 0.043 and g 3 = 0.071 eV from an analysis of the infrared spectrum of the isolated dimer (BEDT-TTF) 2 2+ [53]. The parameters estimated from the infrared spectra were very scattered (g 2 ~ 0.007-0.039 eV and g 3 = 0.007-0.081 eV) depending upon the compounds [54].…”

Section: Electron-molecular Vibration (Emv) Coupling In Bedt-ttfmentioning

confidence: 99%

“…The coupling constant in BEDT-TTF is estimated in refs. [43,53]. The coupling constants of ν 2 and ν 3 were respectively estimated to be g 2 = 0.043 and g 3 = 0.071 eV from an analysis of the infrared spectrum of the isolated dimer (BEDT-TTF) 2 2+ [53].…”

Section: Electron-molecular Vibration (Emv) Coupling In Bedt-ttfmentioning

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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Experimental determination ofBEDT−TTF+elec

Cited by 47 publications

References 32 publications

Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants

Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants

Lattice dynamics and electron-phonon coupling in theβ−(BEDT−TTF)2I3
Girlando
¹
,
Masino
²
,
Visentini
³

et al. 2000
Phys. Rev. B
35
1
38
0
View full text Add to dashboard Cite

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

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Experimental determination ofBEDT−TTF+elec

Cited by 47 publications

References 32 publications

Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants

Temperature dependence of the magnetic susceptibility for triangular-lattice antiferromagnets with spatially anisotropic exchange constants

Lattice dynamics and electron-phonon coupling in theβ−(BEDT−TTF)2I3Girlando1, Masino2, Visentini3 et al. 2000Phys. Rev. B351380View full textAdd to dashboardCite

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

Contact Info

Product

Resources

About

Lattice dynamics and electron-phonon coupling in theβ−(BEDT−TTF)2I3
Girlando
¹
,
Masino
²
,
Visentini
³

et al. 2000
Phys. Rev. B
35
1
38
0
View full text Add to dashboard Cite