Inelastic neutron scattering study of one-dimensional inorganic conductors

Monçeau, P.; Bernard, L.; Currat, R.; Lévy, F.; Rouxel, J.

doi:10.1016/0379-6779(87)90458-9

Cited by 14 publications

(11 citation statements)

References 6 publications

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“…The crosses show the LA data from neutron ͑TAS͒ measurements at Tϭ200 K by Monceau et al, 7 which follow closely the monocrystal-IXS data, apart from a slightly steeper slope at low indicating some stiffening with decreasing temperature. The longitudinal sound velocity calculated from the low-LA data yields 4.5 km/sec for the IXS data (Tϭ295 K) and the slightly higher value of 5.4 km/sec for the TAS data (Tϭ200 K).…”

supporting

confidence: 55%

“…In the TAS study in the (0,2,0) BZ, the TA contribution is observed via double-scattering events ͑Bragg scattering plus phonon͒. 7 The agreement between the TAS and IXS data is reasonable in view of the difference in sample temperature and the possibility of TA 2 contamination in the TAS data. Figure 2 shows some typical energy ͑constant-Q) scans from the IXS measurements covering the Stokes and the anti-Stokes lines ͑phonon annihilation and creation, respectively͒ of the acoustic phonon contribution.…”

mentioning

confidence: 90%

“…Monocrystals of NbSe 3 grow in the form of whiskers with only very small cross sections ͑typically less than 0.1 mmϫ5 m), which made NbSe 3 essentially inaccessible to studies of the lattice-and CDW-related dispersions by neutron scattering techniques. So far only one TAS study of the longitudinal acoustic ͑LA͒ branch propagating along the Q1D direction has been performed by Monceau et al 7 on a bunchlike assembly of 10 4 -10 5 NbSe 3 crystals aligned along the Q1D direction.…”

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Dynamics in the charge-density-wave systemNbSe3using inelastic x-ray scattering with meV energy resolution

et al. 2002

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We present a study of the ambient and low-temperature dynamics on a single-crystalline sample of NbSe 3 using meV-resolution inelastic x-ray scattering. Two phonon branches ͑LA, TA 1 ) propagating along the system's quasi-one-dimensional direction b ជ * have been determined. The low-temperature data indicate the absence of a Kohn anomaly, similar to the case of (TaSe 4 ) 2 I, but at variance with other quasi-one-dimensional charge-density-wave systems ͑KCP, K 0.3 MoO 3 ) investigated so far.Charge-density-wave ͑CDW͒ states in quasi-onedimensional ͑Q1D͒ metallic systems have been the object of intense studies over the last 25 years. However, detailed information about the systems' lattice and CDW dynamics is still quite scarce. To a large extent this is due to the generally very small size of monocrystalline samples of CDW compounds, often too small for techniques like inelastic neutron scattering. Only the dynamics of three CDW systems, available in cm 3 -sized single crystals, have been accessible so far: the platinum-chain compound KCP, 1,2 the blue bronze K 0.3 MoO 3 , 3,4 and (TaSe 4 ) 2 I. 5 The Peierls instability leading to the CDW state is characterized by the opening of an electronic gap at the Fermi level and by a strong softening ͑Kohn anomaly͒ in the lowenergy phonon spectrum at the CDW-modulation wave vector qϭ2k F , where k F is the Fermi wave vector. As shown by Lee et al., 6 below the Peierls transition temperature T P , this soft mode splits up into two branches corresponding to CDW-amplitude excitations ͑amplitudon͒ and CDW-phase excitations ͑phason͒. The latter is expected to stay at zero excitation energy at qϭ2k F or to take up very low, but finite energies related to CDW-pinning by impurities in the system.The Kohn anomaly (TϾT P ) and the CDW dynamics (T ϽT P ) have indeed been observed in KCP, 1,2 as well as in K 0.3 MoO 3 , 3,4 using inelastic neutron scattering ͓three-axis spectroscopy ͑TAS͔͒. Contrary to these results, a thorough TAS study on (TaSe 4 ) 2 I revealed only a very limited phonon softening upon cooling towards T P and no evidence of phason-amplitudon decoupling below T P . 5 Here we present inelastic x-ray scattering ͑IXS͒ measurements on the CDW system NbSe 3 . Monocrystals of NbSe 3 grow in the form of whiskers with only very small cross sections ͑typically less than 0.1 mmϫ5 m), which made NbSe 3 essentially inaccessible to studies of the lattice-and CDW-related dispersions by neutron scattering techniques. So far only one TAS study of the longitudinal acoustic ͑LA͒ branch propagating along the Q1D direction has been performed by Monceau et al. 7 on a bunchlike assembly of 10 4 -10 5 NbSe 3 crystals aligned along the Q1D direction.Additionally, a Raman study of room-temperature optical lattice excitations is reported by Wieting et al. 8 The monoclinic Q1D compound NbSe 3 ͑space group P2 1 /m) undergoes two successive Peierls transitions at T P1 ϭ145 K and T P2 ϭ59 K. Below T P1 it develops a CDW superstructure with a modulation wave vector q ជ 1 ϭ(0,0.241,0) to which is a...

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confidence: 55%

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confidence: 90%

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confidence: 99%

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Dynamics in the charge-density-wave systemNbSe3using inelastic x-ray scattering with meV energy resolution

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“…18,19 Additional measurements below T P are in progress. 20 Clear evidence for a low-frequency inelastic feature is observed: The TA mode (T=300 K) measured at 70 ± 10 GHz (but at 35 GHz on another sample 19 ) becomes critically damped at T P . Below 7]p a propagating mode is observed in the same frequency range which we interpret as the pinned phason mode.…”

Section: C^3n^k B (T/9^j^(x^x 0 )Nx 2 E X /(E X^l ) 2 ]Dx Fmentioning

confidence: 91%

Contributions of Phasons and of Low-Energy Excitations to the Specific Heat of the Quasi One-Dimensional Compound(TaSe4)2
Biljaković
¹
,
Lasjaunias
²
,
Zougmoré
³

et al. 1986
Phys. Rev. Lett.
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66
2
16
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Measurements of the specific heat of quasi one-dimensional conductors, (TaSe 4 ) 2 I and (NbSe 4 ) 3 I, between 0.1 and 8 K, are reported. Whereas no deviation from the P law occurs at low temperature for (NbSe 4 ) 3 I, we have measured two anomalies in (TaSe^I: an excess heat capacity with a peak at J= 1.75 K and a specific heat which follows a P 2 law below 0.4 K. We ascribe this excess heat capacity to the charge-density-wave phase excitations above their pinning frequency in the insulating Peierls state (rp = 263 K).PACS numbers: 65.40.Em, 63.20.Dj, 63.50, + x, 72.15.Nj It is now well known that many few-dimensional compounds are unstable and undergo a Peierls transition at a critical temperature, T ? } This instability is characterized by the opening of an electronic gap at the Fermi level, by a softening in the phonon spectrum at 0==2/c F with A: F the Fermi wave vector, and by a modulation of the electron charge density with the same periodicity called a charge-density wave (CDW). Below T ? the soft-phonon branch splits into two different modes 2 " 4 : an opticlike amplitude mode and an acousticlike phase mode. For ideal one-dimensional conductors, when Q is incommensurate with the lattice, the phase mode or phason exists at zero frequency and corresponds to the current provided by the sliding motion of the CDW as proposed by Frohlich. 5 In real systems, as shown by Lee, Rice, and Anderson, 3 the gapless character of the phase mode is destroyed through various mechanisms, especially impurity pinning.Recently, the interest has focused on several families of one-dimensional inorganic compounds undergoing Peierls transitions, namely, transition-metal trichalcogenides (NbSe 3 , TaS 3 ), blue bronze, and halogenated transition-metal tetrachalcogenide (TaSe^L 6 In these compounds an extra dc current appears when the applied electric field is higher than a threshold value (typically 0.1-1 V/cm). This extra conductivity has been ascribed to Frohlich-type conduction when the CDW becomes unpinned and moves through the crystal. 6 By complex-impednace measurements in the millimeter-wave range the pinned sliding model for NbSe 3 and TaS 3 is found to be overdamped with a spectral response in the megahertz-gigahertz range, 7 whereas for (TaSe^I this mode is underdamped, indicating a pinning frequency 8 of 35 GHz or 1.7 K. The frequency of this pinned mode is just in the right frequency range to allow for the detection of CDW excitations by thermodynamical measurements.Hereafter we report on heat-capacity measurements on (TaSe^I and, for comparison, on (NbSe 4 ) 3 I. These compounds consist of parallel MSe 4 chains well separated from one another by halogen atoms. In each MSe 4 chain the metal atom is located at the center of a rectangular antiprism of eight Se atoms. The d z2 band filling of the transition metal M can be varied according to the composition. This change in band filling leads to quite different structural and electrical properties: (TaSe 4 ) 2 I and (NbSe 4 )ioI 3 undergo a Peierls transition at T P ...

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“…Only an earlier measurement of the longitudinal acoustic branch propagating along the chain direction has been performed on a bunch-like assembly of 10 4 -10 5 NbSe 3 crystals aligned along the chain direction [12]. NbSe 3 undergoes two CDWs, an upper one at T P 1 = 145 K and a second one at T P 2 = 59 K. The inelastic X-ray scattering (IXS) is a powerful technique for the study of phonon dispersion on samples only available in very small quantities.…”

Section: Inelastic Neutron Scattering Experimentsmentioning

confidence: 99%

Inelastic neutron scattering study of one-dimensional inorganic conductors

Cited by 14 publications

References 6 publications

Dynamics in the charge-density-wave systemNbSe3using inelastic x-ray scattering with meV energy resolution

Dynamics in the charge-density-wave systemNbSe3using inelastic x-ray scattering with meV energy resolution

Contributions of Phasons and of Low-Energy Excitations to the Specific Heat of the Quasi One-Dimensional Compound(TaSe4)2
Biljaković
¹
,
Lasjaunias
²
,
Zougmoré
³

et al. 1986
Phys. Rev. Lett.
Self Cite
66
2
16
0
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Nature of the Peierls transition in charge density wave systems: Strong coupling versus weak coupling

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Inelastic neutron scattering study of one-dimensional inorganic conductors

Cited by 14 publications

References 6 publications

Dynamics in the charge-density-wave systemNbSe3using inelastic x-ray scattering with meV energy resolution

Dynamics in the charge-density-wave systemNbSe3using inelastic x-ray scattering with meV energy resolution

Contributions of Phasons and of Low-Energy Excitations to the Specific Heat of the Quasi One-Dimensional Compound(TaSe4)2Biljaković1, Lasjaunias2, Zougmoré3 et al. 1986Phys. Rev. Lett.Self Cite662160View full textAdd to dashboardCite

Nature of the Peierls transition in charge density wave systems: Strong coupling versus weak coupling

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Contributions of Phasons and of Low-Energy Excitations to the Specific Heat of the Quasi One-Dimensional Compound(TaSe4)2
Biljaković
¹
,
Lasjaunias
²
,
Zougmoré
³

et al. 1986
Phys. Rev. Lett.
Self Cite
66
2
16
0
View full text Add to dashboard Cite