Far-infrared powder absorption measurements of some tetramethyltetraselenafulvalene salts [(TMTSF<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>X]

Eldridge, J. E.; Homes, C. C.; Bates, Frances E.; Bates, Gordon S.

doi:10.1103/physrevb.32.5156

Cited by 30 publications

(9 citation statements)

References 30 publications

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“…This Grűneisen parameter is more than one order of magnitude larger than the one deduced from the frequency shift of the low-frequency TMTSF lattice modes measured by infrared absorption in PF 6 -H12 and PF 6 -D12. 43 This large (PF 6 ) value consistently confirms that the lowtemperature thermal expansion of (TMTSF) 2 PF 6 is dominated by the librational motion of the PF 6 units.…”

Section: B Thermal Expansion and Anion Librationsupporting

confidence: 64%

“…44,45 It is also close to the frequency of the A u and B u translational and librational TMTSF lattice modes measured by far-infrared absorption in PF 6 -H12 and PF 6 -D12. 43 One thus expects important coupling between all these lattice modes. In particular, translational and librational motions of the TMTSF molecule should modify the geometry of the methyl-group cavity in which the anion rotates and vice versa.…”

Section: B Thermal Expansion and Anion Librationmentioning

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: B Thermal Expansion and Anion Librationsupporting

confidence: 64%

Section: B Thermal Expansion and Anion Librationmentioning

confidence: 99%

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

et al. 2013

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“…In fact, they always show up below T CO when inversion symmetry is removed, while anion translations should already be infrared active even in centrosymmetric systems. The fact that these translational ionic modes are missing in the infrared spectra has been also reported for the isostructural Bechgaard (TMTSF) 2 X salts by Eldridge et al [112], whose band assignments was supported by isotope-substitution shifts. Of course, we cannot rule out the possibility that these modes occur at energies lower than 40 cm −1 due to their massive ionic components and the relatively large and soft anion cages.…”

Section: Far-infrared Spectrasupporting

confidence: 57%

Comprehensive Optical Investigations of Charge Order in Organic Chain Compounds (TMTTF)2X

et al. 2012

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Charge ordering in the (TMTTF) 2 X salts with centrosymmetric anions (X = PF − 6 , AsF − 6 , SbF − 6 ) leads to a ferroelectric state around 100 K. For the first time and in great completeness, the intra-and intermolecular vibrational modes of (TMTTF) 2 X have been investigated by infrared and Raman spectroscopy as a function of temperature and pressure for different polarizations. In this original paper, we explore the development and amount of charge disproportionation and the coupling of the electronic degrees of freedom to the counterions and the underlying lattice. The methyl groups undergo changes with temperature that are crucial for the anion cage formed by them. We find that the coupling of the TMTTF molecules to the hexafluorine anions changes upon cooling and especially at the charge-order transition, indicating a distortion of the anion. Additional features are identified that are caused by the anharmonic potential. The spin-Peierls transition entails additional modifications in the charge distribution. To complete the discussion, we also add the vibrational frequencies and eigenvectors based on ab-initio quantum-chemical calculations.

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“…We note that the particularly high density of low-lying phonons observed for the c direction are also likely complemented by zone folded modes due to the incommensurate chain-ladder relationship and charge order Peierls distortion that modulates the chain and ladder symmetries while maintaining the same overall crystal structure [32,53,54]. The zone folding phenomenon is well documented in other low-dimensional systems exhibiting charge ordering [55][56][57][58]. In SCO, the effect has previously been noted by the appearance of new phononlike Raman modes below T co , in the vicinity of 6-18 THz [51].…”

Section: Resultsmentioning

confidence: 58%

Effects of Ca substitution on quasiacoustic sliding modes in Sr14−xCaxCu24O41

et al. 2019

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The low-energy lattice dynamics of the quasiperiodic spin-ladder cuprate Sr14-xCaxCu24O41 are investigated using terahertz frequency synchrotron radiation. A high density of low-lying optical excitations is present in the 1-3 THz energy range, while at least two highly absorbing excitations stemming from long-wavelength acoustic oscillations of the incommensurate chain and ladder sublattices, are observed at subterahertz frequencies. The effects of Ca substitution on the subterahertz quasiacoustic sliding mode gaps is investigated using coherent synchrotron radiation. Analysis of the results suggest increasing substitution of Sr for Ca is accompanied by a transfer of spectral weight between sliding modes associated with different chain-ladder dynamics. The observation is consistent with a transfer of hole charges from the chains to the ladders and modification of the sublattice dimensions following Ca substitution. The results are discussed in context to the significance of low-lying vibrational dynamics and electron-phonon coupling in the superconducting state of certain quasiperiodic systems.

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Far-infrared powder absorption measurements of some tetramethyltetraselenafulvalene salts [(TMTSF)2X]

Cited by 30 publications

References 30 publications

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

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

Comprehensive Optical Investigations of Charge Order in Organic Chain Compounds (TMTTF)2X

Effects of Ca substitution on quasiacoustic sliding modes in Sr14−xCaxCu24O41

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