X-Ray Diffuse Scattering Study of Some (TMTSF)<sub>2</sub>X and (TMTTF)<sub>2</sub>X Salts

Pouget, Jean‐Paul; Moret, R.; Comès, R.; Bechgaard, K.; Fabre, Jean‐Marc; Giral, L.

doi:10.1080/00268948208070995

Cited by 147 publications

(79 citation statements)

References 15 publications

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“…This increase of lattice rigidity should decrease the electron-phonon coupling between the acoustic-like BOW stack deformation and the high temperature 1D 2k F electronic instability observed in the Bechgaard salts. In particular, the 55 K lattice hardening nicely explains the drop of intensity of the 2k F BOW response exhibited by x-ray diffuse scattering data below T * * ∼ 50 K. 12,13,18,19 Similarly, a drop of the 2k F BOW diffuse scattering intensity is observed below ∼50 K in the AsF 6 salt, 47 which behaves as the PF 6 salt. At the present stage of our investigation, there is no clear evidence that the structural modification occurring at ∼55 K is due to a symmetry breaking.…”

Section: The Structural Change Around 55 Kmentioning

confidence: 73%

“…At high temperature the coherent charge transport is confined (1D behavior) to the stack direction a where (TMTSF) 2 PF 6 behaves as a Tomonaga-Luttinger liquid. 9,10 In this regime this salt exhibits both 2k F SDW 11 and bond-order-wave (BOW) 12,13 1D instabilities. Upon cooling, the one-particle properties exhibit a 1D to two-dimensional (2D) crossover around 100 K (T * ), the temperature below which the charge transport becomes coherent in the (a, b) TMTSF layers.…”

Section: Introductionmentioning

confidence: 99%

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Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

et al. 2013

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We present a detailed low-temperature investigation of the statics and dynamics of the anions and methyl groups in the organic conductors (TMTSF) 2 PF 6 and (TMTSF) 2 AsF 6 (TMTSF: tetramethyl-tetraselenafulvalene). The 4 K neutron-scattering structure refinement of the fully deuterated (TMTSF) 2 PF 6 -D12 salt allows locating precisely the methyl groups at 4 K. This structure is compared to the one of the fully hydrogenated (TMTSF) 2 PF 6 -H12 salt previously determined at the same temperature. Surprisingly, it is found that deuteration corresponds to the application of a negative pressure of 5 × 10 2 MPa to the H12 salt. Accurate measurements of the Bragg intensity show anomalous thermal variations at low temperature both in the deuterated PF 6 and AsF 6 salts. Two different thermal behaviors have been distinguished. Small Bragg-angle measurements reflect the presence of low-frequency modes at characteristic energies θ E = 8.3 K and θ E = 6.7 K for the PF 6 -D12 and AsF 6 -D12 salts, respectively. These modes correspond to the low-temperature methyl group motion. Large Bragg-angle measurements evidence an unexpected structural change around 55 K, which probably corresponds to the linkage of the anions to the methyl groups via the formation of F. . .D-CD 2 bonds observed in the 4 K structural refinement. Finally we show that the thermal expansion coefficient of (TMTSF) 2 PF 6 is dominated by the librational motion of the PF 6 units. We quantitatively analyze the low-temperature variation of the lattice expansion via the contribution of Einstein oscillators, which allows us to determine for the first time the characteristic frequency of the PF 6 librations: θ E ≈ 50 K and θ E = 76 K for the PF 6 -D12 and PF 6 -H12 salts, respectively.

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Section: The Structural Change Around 55 Kmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

et al. 2013

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“…High-temperature 1D 4k F fluctuations are commonly observed in quarter-filled organic salts based on the TCNQ or DCNQI acceptor derivatives, such as Qn(TCNQ) 2 , 67 (DMe-DCNQI) 2 Ag, 41 and (DI-DCNQI) 2 Ag, 43 or on the TTF or TSF donor derivatives, such as TMTTF-DMTCNQ and TMTSF-DMTCNQ, 62 the only exception being the (TMTTF) 2 X series. 68 These 4k F fluctuations are also systematically observed when the band filling is very close to one-quarter, such as in (TMTTF) 2 Bromanil, 69 DBTTFTCNQCl 2 , 70 BTDMTTF-TCNQ, 71 , and the solid solution (NMP) x (Phen) 1-x TCNQ for x ∼ 0.5. 72 In TMTSF-DMTCNQ and BTDMTTF-TCNQ the high-temperature 4k F fluctuations vanish upon cooling, but in the other salts they condense either into a high-temperature 4k F modulation or give rise to a 4k F short-range order in the presence of disorder.…”

Section: A Pretransitional Effectsmentioning

confidence: 99%

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(
Foury-Leylekian
¹
,
Auban-Sensier
²
,
Coulon
³

et al. 2011
Phys. Rev. B

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The 2:1 family of organic salts (o-DMTTF) 2 X (X = Cl, Br, I) exhibits regular stacks and a high-symmetry structure, which provide a perfect three-quarter-filling-band system allowing a rich phase diagram in the presence of strong electronic correlations. In this paper, we present a detailed study of this series combining complementary experimental techniques such as resistivity, thermopower, electron spin resonance, static magnetic measurements, and x-ray diffraction. In particular, we show that at ambient pressure (o-DMTTF) 2 X with X = Br and Cl undergoes two successive phase transitions setting successively a 4k F charge density and bond order wave order, then a spin-Peierls (SP) ground state. We discuss the symmetry of these phases and its relationship with the transport and magnetic properties. These phases are also followed under pressure by transport experiments, allowing the establishment of a generic phase diagram for this series of salts, where, with the onset of a one-dimensional to three-dimensional deconfinement transition, the 4k F order vanishes and the SP ground state transforms into a Peierls one. Interestingly, this phase diagram differs significantly from the one previously reported in other three-quarter-filled systems such as (TMTTF) 2 X and δ-(EDT-TTF-CONMe 2 ) 2 X.

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“…This may explain why no similar elastic anomaly is detected on either D 12 or H 12 sample at the charge ordering scale, T CO , in the insulating state (see Figure 1). As for spin degrees of freedom, NMR and spin susceptibility data display essentially gapless excitations in this sector [7,8,10], down to the temperature scale of 60 K where, according to early X-ray measurements, lattice precursors of the SP transition appear [13], and below which spins and lattice become strongly coupled. Spins are known to couple easily to strain in various magnetic systems so as to induce a monotonic softening on the compressibility modulus whose temperature dependence correlates with the regular increase of magnetic susceptibility with temperature above the transition temperature.…”

Section: Resultsmentioning

confidence: 99%

“…In the H 12 -PF 6 salt, the observation of X-ray 2k F diffuse scattering indicates the presence below ∼ 60 K of onedimensional lattice precursors of the SP transition [13]; these eventually lead to a reduction of spin degrees of freedom akin to a spin pseudogap [16], as exhibited by EPR susceptibility [7,8] If the role of lattice degrees of freedom in the stabilization of the CO ground state is relatively well documented in the PF 6 and AsF 6 salts [17,18], the situation is not so clear for the SP transition. Except for X-ray diffuse scattering for the lattice precursors below 60 K, which condense into Bragg spots at T SP [13], and anomalies in the thermal expansivity data [17,18], the nature of the magneto-elastic coupling involved in the SP instability remains poorly understood in these compounds. As far as the charge degrees of freedom are concerned, they appear largely decoupled from the spins in the non ordered temperature region.…”

Section: Introductionmentioning

confidence: 99%

Magnetoelastic coupling in the spin-Peierls ground state of hydrogenated and deuterated (TMTTF)2PF6salts

et al. 2012

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We report an ultrasonic study of the magneto-elastic coupling of the hydrogenated and deuterated (TMTTF)2PF6 organic salts. For both salts the temperature dependence of the longitudinal velocity along the c * axis displays a monotonic stiffening of the C33 compressibility modulus upon cooling. Below the characteristic temperature scale 40 K the modulus stiffening becomes markedly enhanced, in concomitance with the reduction of spin degrees of freedom previously seen in magnetic measurements as low dimensional precursors of the spin-Peierls transition. The magneto-elastic coupling appears to be much weaker in the hydrogenated salt due to the highly inhomogeneous elastic behavior induced by the proximity of the charge ordering transition to the spin-Peierls phase. For the deuterated salt, an important anomaly in the ultrasound velocity is observed below the spin-Peierls transition temperature TSP in agreement with scaling of the elastic deformation with the spin-Peierls order parameter. In spite of the weakly inhomogeneous character of the spin-Peierls phase transition, the magnetic field dependence of TSP is well captured with the mean-field prediction for the lattice distorted Heisenberg spin chain.

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X-Ray Diffuse Scattering Study of Some (TMTSF)₂X and (TMTTF)₂X Salts

Cited by 147 publications

References 15 publications

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(
Foury-Leylekian
¹
,
Auban-Sensier
²
,
Coulon
³

et al. 2011
Phys. Rev. B

Magnetoelastic coupling in the spin-Peierls ground state of hydrogenated and deuterated (TMTTF)2PF6salts

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X-Ray Diffuse Scattering Study of Some (TMTSF)2X and (TMTTF)2X Salts

Cited by 147 publications

References 15 publications

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

Low-temperature structural effects in the (TMTSF)2PF6and AsF6Bechgaard salts

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(Foury-Leylekian1, Auban-Sensier2, Coulon3 et al. 2011Phys. Rev. B

Magnetoelastic coupling in the spin-Peierls ground state of hydrogenated and deuterated (TMTTF)2PF6salts

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Product

Resources

About

X-Ray Diffuse Scattering Study of Some (TMTSF)₂X and (TMTTF)₂X Salts

Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(
Foury-Leylekian
¹
,
Auban-Sensier
²
,
Coulon
³

et al. 2011
Phys. Rev. B