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The isospinel structural compounds CuIr2−xMxS4 (M=W/Mn) are designed to study the different influences on the 5 d electrons of Ir. W ions acting as W4+ in CuIr2−xWxS4, while Mn ions act as Mn2+ in CuIr2−xMnxS4. The suppression of W4+ on the Peierls-like phase transition is more effective than that of Mn2+. The influences of W4+ and Mn2+ on the magnetization are different. The doping of W4+ causes diamagnetism even before the Peierls-like phase transition in CuIr2−xWxS4 system, while Mn2+ produces a paramagnetic background in the CuIr2−xMnxS4 system.

The specific heat of the quasi-one-dimensional charge-density-wave (CDW) compound TlO3MoO3 has been measured using an adiabatic continuous heating method from 100 to 220 K. A specific heat jump associated with the Peierls phase transition occurs at 172.3 K. A good scaling relation between the excess specific heat and the susceptibility is found between 140 K and 190 K. Further analysis indicates that the width of the critical region of Tl0.3MoO3 is about 10 K and the specific-heat critical behavior can be well described by the three-dimensional XY model. (c) 2006 Elsevier Ltd. All rights reserved.

We report on the reflectance of blue bronze crystals in the visible frequency range as a function of temperature. The observed large oscillations in the reflectance at all wavelengths at temperatures near the Peierls transition are interpreted as interference effects stemming from a surface layer. It is found that the surface layer, which appears to be tied to fluctuations, can be as much as 1.6 microns thick.

In the near vicinity of Peierls transition temperature TP, we have measured the V–I characteristics of the quasi-one-dimensional conductor TaS3 under dark and photo-irradiation conditions. It is found that a significant enhancement of CDW current occurs only around the threshold voltage Vt under photo-irradiation. This effect can be interpreted as a result of screening of pinning potential for CDW condensate by photo-excited quasi-particles (QP's). Further the distribution of pinning potential intensity is reflected in the behavior of V–I characteristics near Vt. Our finding suggests that the strength of pinning potential can be controlled by the photo-excited QP's in quasi-1D conductors.

The authors have studied the soliton generation process in the quasi-one-dimensional platinum Rb 2 Pt(CN) 4 (FHF) 0.4 compound. Under the Peierls-transition temperature T P , a periodic lattice distortion accompanied by a charge density wave (CDW) with commensurability N =5 condensates. Local depinning of the CDW generates a soliton–antisoliton pair. The energy spectrum of the 5d z 2 Pt electrons along with charges and spins of all soliton types are calculated.

The effects of radio frequency (rf) fields on charge density wave current conversion were studied by normal and transposed measurements. In contrast to the strong suppression of the dc threshold fields, the suppression of phase slip voltages was less effective. The phase slip voltages can be even larger in rf fields. Oscillations with the magnitude of the rf fields were both observed in threshold voltages and phase slip ones.

We show that ensembles of mesoscopic Peierls rings in a magnetic flux possess properties completely different from those of isolated rings. A new, unusual magnetic transition between dia- and paramagnetic states occurring in ensembles of rings is found. It can be experimentally studied by means of a SQUID technique.

We predict that the minimum size of a Peierls dimerized chain with weak electron-phonon coupling can be in (sub)micrometer range and be there-fore detectable in mesoscopic systems. We suggest perylene radical cation salts as possible materials and the non-linear optical absorption as a possible technique of experimental observation.

The effect of cationic substitution on a spin Peierls (SP) transition in CuGeO3 single crystals is studied by susceptibility measurements. In-chain and off-chain doping were carried out by substituting cobalt in the copper site and gallium in the germanium site respectively. SP transition is found to be very sensitive to nature and concentration of dopant. Increasing gallium concentration induces a systematic reduction in transition temperature (TSP) whereas magnetic impurity cobalt causes its drastic reduction. 1 at% cobalt is sufficient to suppress SP transition completely Influence of magnetic impurity with high spin value disrupting the spin-1/2 chain is discussed

High-energy-resolution angle resolved photoemission measurements have been carried out on monophosphate tungsten bronzes with pentagonal tunnels (PO2)4(WO3)2m for different values of m (6 ≤ m ≤ 12). A broad angle independent feature is observed near the Fermi level whose position exhibits a systematic trend: the peak shifts to higher binding energy with increasing m. These experimental data are not corroborated by band calculations which predict a narrow band whose energy position moves towards the Fermi level with increasing m. Therefore the spectroscopic properties cannot be described within a one-electron band formalism. Finally, the temperature dependence of the spectra only shows the usual Fermi level broadening and a small shift of the main feature. No evidence of spectral modifications induced by Peierls transition for low m values is observed.

We have measured anelastic properties of the Peierls transition over three samples of (TaSe4)2I containing different defect concentration (Tp = 242.5 K and 255 K). We observed a huge change in the elastic shear modulus ( ΔG G ∼ 12% ) accompanied by a significant internal friction peak (ΔQ−1 ∼ 10−2) at 1 Hz. Due to the randomness of the calculated critical exponents we propose that the transition develops as a first order one, perpendicular to the chain direction.

We present an X-ray diffuse scattering study of the q2-pretransitional structural fluctuations of the low temperature Tc2 Peierls transition in the trichalcogenide NbSe3. In the (a,b) layers, these fluctuations have about the same anisotropy as the q1-fluctuations of the high temperature Tc1 Peierls transition. However, in the interlayer c∗ direction they are more correlated. We suggest that screening of Coulomb interactions between charge density waves, that we take as responsible for the three-dimensional ordering, explains this difference.

Critical temperature of metal-insulator transition (Peierls transition) of metallic carbon nanotube (tube (n, n); see [4] and [5] with respect to the notation of tube) has been estimated considering the electron-phonon interaction. Specifically for tube (5, 5) with a diameter of ∼ 7 A, it has been found out that the Peierls-transition temperature Tp is equal to 9.1 K and the energy gap Eg to 1.26 × 10−3 eV at T = 0 K.

The transition temperature of the spin - Peierls transition in single crystals of the inorganic linear chain compound CuGeO 3 is determined in magnetic fields up to 5.5T. A decrease quadratic with the applied field is detected which differs by up to 16% for different orientations of the magnetic field with respect to the crystal axes. By taking into account the principal g - factors of Cu 2+ in CuGeO 3 , a unique value for the magnitude of the decrease is derived which is in good agreement with the predictions of the Hartree-Fock theory of Bulaevskii, Budzin and Khomskii.

The effect of doping with nonmagnetic Zn2+ ions on the spin-Peierls transition in pseudo-one-dimensional CuGeO3 has been studied by ESR intensity and electron spin-lattice relaxation time measurements as functions of temperature. The results show that impurity doping in Cu0.97Zn0.03GeO3 reduces the magnetic energy gap much more than the spin Peierls transition temperature. Our results thus provide experimental support for recent theoretical predictions that a gapless spin-Peierls state may take place in Zn+ doped CuGeO3 at intermediate doping levels in analogy to gapless superconductivity.

We have performed torsion measurements in (TaSe 4 ) 2 I in the temperature range 110–290 K and 5.10 −3 –10 Hz measuring frequency. We have always found a dip in modulus at the Peierls transition and that deformation of measurement gives additional response in modulus and internal friction spectra. These results are compared with existing models.

The electronic excitation density of states of Rb 0.3 MoO 3 in the Peierls type charge density wave state has been measured at a specified point of the surface image taken by scanning tunneling microscopy (STM). The peierls gap 2Δ is roughly estimated to be 140meV, which is significantly larger than the value expected from the BCS theory even after the fluctuation effect is taken into account. The lattice image of Mo 8 O 23 is also taken at the temperature T∼280K.

The electrical resistivity and the lattice parameters have been studied as a function of pressure on the quasi-twodimensional purple bronze KMo 6 O 17 which shows a Peierls transition towards a commensurate charge density wave state. The Peierls temperature is found to be first slightly decreased for pressures smaller than 6 kbar, then strongly increased above. This increase is associated to an anomalous contraction of the lattice parameters in the plane of the layers. The corresponding large increase of the compressibility above 16 kbar at 300 K is associated to the pretransitional regime of the Peierls transition as a function of pressure. These results are attributed mainly to an improved nesting of the Fermi surface under pressure.

The crystal structures of compounds of the right hand side of the Mendeleiev table can be easily understood in terms of their electronic structure. The bonding mechanism is of ppσ type and the expected simple cubic structure is subsequently deformed by a Peirls transition: some bonds are shortened and some others are elongated among the directions of the axes of the cube. The alternation of short and long bonds is driven by the electron/atom ratio. Using simple theoretical arguments, we show that the periodicity of deformation is simply related to the average number N p of p electrons. If the filling of the p band isN p 6=nmwhere n and m are prime numbers, the structure shows a m-fold periodicity. We show that, up to very large m values, this rule is confirmed without any exception by an important series of compounds including As x Te 1-x , Sb x Te 1-x , Bi x Se 1-x , Bi x Te 1-x and As 2 Ge x Te 3+x .

We have measured the Peierls transition temperature T c , the threshold field for deipinning the charge density wave E c and E.P.R. spectra at 10 GHz and analyzed Atomic Absorption measurements of (TaSe 4 ) 2 I doped with 2% Mn in samples grown with changing the excess iodine in the blister. Our results show that Mn ions enter the structure in two different states (cluster and isolated ions) and that isolated ions enter in very small quantities (approx. 1 ppm).

The frequency dependent conductivity of quasi-one-dimensional inorganic conductors under Peierls transition experimentally observed is connected with collective transport of charge density wave (CDW). The dynamics of incommensurate CDW under impurity pinning has been described by two-mode model: low-frequency pinning mode and high-frequency phason one. The main feature of the model is that the modes are connected and displacements of CDW caused by both modes are sewn together at the pinning centers. The random distribution of model parameters is taken into consideration. Comparison between experimental data and calculated results based on the model proposed are in good quantitative agreement.

The ternary charge transfer salt, TMS TCNQ I 1 3 3, where TMS is trimethyl sulphonium and TCNQ is tetracyanoquinodimethane, shows a weakly metallic conductivity at room temperature, which falls at lower temperatures. We report measurements of the electrical and magnetic properties, and consider that this salt undergoes a Pejerls transition at around 160 K, and that disorder in the crystal structure limits conductivity in the metallic state and broadens the Peierls transition.

The temperature dependence of thermoelectric power has been measured in the quasi-one dimensional charge density-wave (CDW) systems (NbSe4)103 I and (TaSe4)2 I. In the (NbSe4)103 I system, the thermopower remains positive throughout the temperature range investigated (120–350 K) whereas for (TaSe4)2 I it changes sign from negative values above the Peierls transition temperature (Tp = 263 K to positive values below Tp. Both these results are in agreement with Hall effect measurements. In addition we deduce from the temperature dependence of thermopower below Tp that there exists larger electron-hole asymmetry (σe/σh) in (NbSe4)103 I as compared to (TaSe4)2 I. The unusual behaviour of thermopower below a temperature (Tm) in these and other incommensurate systems is attributed to CDW drag effects of Umklapp type.

Simple analytical expressions are found for both the free energy and elasticity of charge- density waves (CDW) in Peierls conductors. The presence of dislocations in the CDW is accounted for phenomenologically by the introduction of energy levels within the Peierls gap, and a modified electroneutrality equation is proposed. The expressions reproduce known theoretical and experimental results concerning both the elasticity of the CDW and the relaxation of metastable states, and also suggest an alternative origin of the Peierls transition in real crystals.

We have investigated the effect of hydrostatic pressure on the resistivity of the quasi-one-dimensional conductor blue bronze, K0.3MoO3, in both the ohmic and nonlinear regimes. The Peierls transition temperature (Tp) and energy gap Δ decrease under pressure with the same rate of ∼ 1%/kbar. The threshold electric field (ET) for sliding charge density wave (CDW) conduction is pressure independent at 77 K up to 17–19 kbars. Above these pressures ET increases. The pressure dependence of the high field resistivity (E

We report our measurement of the temperature dependence of threshold field E T on a thin Rb 0.30 MoO 3 sample from 88K to the vicinity of Peierls transition temperature 180K. A sharp peak of E T was observed at 160K with a monotonously changing background, and the rapid increase of E T near 180K was also observed. We also obtained some preliminary results on the high field limit of the conductivity contributed by CDW.

Mossbauer studies have been performed between 77K and 300K on powders of the quasi-two dimensional oxide 57 Fe-doped γ -Mo 4 O 11 . The spectra show four quadrupolar doublets. The observed anomaly of the center shift in the vicinity of the Peierls-charge density wave transition at 100K is ascribed to a decrease of the Debye-Waller factor of two molybdenum sites only. The associated hysteresis phenomena are discussed in terms of interactions between slowly diffusing 57 Fe impurities and the charge density wave.

(TaSe4)2I is a quasi-1 D conductor which undergoes a Peierls transition at Tp = 260 K [1]. Phonon softening at 2kF (Fermi momentum) induces lattice modulations associated with an electron charge density wave (CDW). Elastic singularities at the Peierls transition are not yet well understood [2]. The associated singularity in the sound velocity examined theoretically by Nakane [3] varies like |T-Tp|−1/2 around Tp.

We study the thermodynamics of a noninteracting electron system with a half filled strongly anisotropic tight binding band in the mean field approximation. This system may exhibit a structural transition dimerizing along the high conductivity direction. The conditions for the instability to occur are given as a function of the degree of anisotropy. The relationship to the behavior of TCNQ salts is discussed.

Raman scattering experiments on K 2 Pt(CN) 4 Br 0.3 · 3H 2 O are reported between 5 and 300 K as a function of temperature. A line of A 1 symmetry detected at 44 cm −1 shows interesting temperature dependent properties. It is concluded from a comparison of the frequency, symmetry, and scattering intensity of this line with theoretical predictions that the excitation concerned represents the amplitude mode of the charge density wave (the line observed in infrared absorption being the phase mode). No Peierls transition is observed, but the results are consistent with a Peierls distortion present at all temperatures. The findings are correlated with inelastic neutron scattering and infrared studies. Finally, the CN stretching modes at 2189 and 2173 cm −1 and the water mode at 3490 cm −1 are studied as a function of temperature.

We have taken bolometric infrared spectra of the charge-density-wave conductor orthorhombic TaS3, doped with niobium and titanium. For transverse polarization, the bolometric signal is roughly proportional to the absorptivity. Niobium doping (∼200 ppm) greatly increases the charge-density-wave depinning field and broadens the Peierls transition, while Ti doping (∼ 10 ppm) has negligible effect. Nevertheless, both types of samples have similar spectra: a large decrease of absorption above the Peierls gap (i.e. smearing of the absorption threshold) and no significant increase in absorption below the gap. The “midgap” absorption line at 500 cm−1 is not affected by doping. Results are discussed in terms of the model of Tutto and Zawadowski.

An experimental study is presented of the specific heat of the spin—Peierls systems TTF-TBT(M), M = Cu, Au. The linear term, γT, expected for the uniform one-dimensional antiferromagnet at low temperatures is observed above the Peierls transition. Specific heat anomalies associated with the transition are found at Tp(Cu) = 12.4K and Tp(Au) = 2.06K. The transition for TTF-BDT(Cu) is mean-field like; whereas the transition for TTF-BDT(Au) is broadened by one-dimensional fluctuation effects.

We explain the anomalous peak of the conductivity by applying the pinning mechanism at T = 0 to the case above the Peierls transition temperature. The longitudinal sound attenuation coefficient (αL) is calculated also. The sound is attenuated essentially through a pair of charge density wave fluctuations.

The influence of the intrachain Coulomb interactions on the Peierls transition is examined. The change of the form of the electronic polarizability at twice the Fermi wavevector, to a power law divergence in the presence of Coulomb interactions, is found to enhance the mean field transition temperature for the Peierls transition.

The occupied position of Fe in the superconducting phase of Fe-doped YBa2Cu2.8807-x was estimated by point charge model. The Mossbauer spectra were measured in the temperature range from 78 K to 273 K. Lattice softenings were found near 110 and 220 K. The observed variations of hyperfine parameters can be considered tobe related to the lattice softening near 110 K. It is suggested that the lattice softening near 110 K is related to the Peierls instability of the one-dimensional Cu(1)−0 chains.

The mean field critical temperature for the spin-Peierls phase transition in the XY antiferromagnetic chain is obtained for nearest and next nearest neighbour exchange interaction. An increase in T c is predicted for next nearest neighbour antiferromagnetic exchange and a decrease is obtained for ferromagnetic exchange. This model is applied to the alkali-TCNQ salts, which are treated in the framework of the highly correlated Hubbard model.

Recent microscopic calculations that explore the Frohlich charge density wave conductivity σF in the region of a mean-field Peierls transition cannot hope to render justice to the far from mean-field situations that obtain experimentally. An approximate theoretical formula for σF that does can be derived on a semi-phenomenological basis, and leads to a crude estimate for the maximum conductivity of one-dimensional metal like TTF-TCNQ.

Dielectric function of quasi-one-dimensional conductor NbSe3 has been measued in the vicinity of Peierls transition near Tp=145K by use of novel technique. The low frequency noise in V/I/ characteristics is attributed to the Gaussian type of position fluctuations of pinned charge density wave (CDW) and fundamental frequency of the noise is found to be identical with spring frequency of restoring forces.

Conductivity measurements on isotopically substituted single crystals of TTF-TCNQ show a relatively large shift in the phase transition temperatures at 52.5 K (T1) and 37.7 K (T3). Deuteration of both TTF and TCNQ chains increases T1 by 0.75 ± 0.15 K, N15 substitution increases T1 by 0.6±0.1 K while deuteration of the TTF chains apparently has no significant effect. Different possible interpretations of these results are briefly discussed.

We present electron spin resonance results on three different conducting phases of the organic conductor based on the planar molecule BEDT-TTF ( bis (ethylenedithio)tetrathiafulvalene) and the anion ReO 4 in different stoichiometries. Both the paramagnetic susceptibility χ as well as the ESR-linewidth Δ H pp may be used to classify the magnetic behaviour in terms of known behaviour of other organic metals. They indicate that the 2:1 phase, which under pressure becomes superconducting, has an anion-ordering assisted metal-insulator transition near 80 K and that the 3:2 phase has a Peierls transition at 88 K, below which two ESR lines are resolved. A third phase, which includes solvent in the crystal lattice, shows no evidence of a transition.

We report non linear transport properties below the metal-insulat transition temperature T° = 263 K in the halogened metal transition tetrachalcogenide (TaSe4)2I. These non linear properties are similar to those of NbSe3 and TaS3 and indicate that (TaSe4)2I is a new compound exhibiting charge density wave transport.

The reduction in Peierls transition temperature in a disordered one dimensional conductor is calculated using the coherent potential approximation. Comments are made on the role of disorder on the three dimensional ordering below the Peierls temperature.

We present X-ray measurements of the distortion wave numbers and their temperature evolution in the blue bronzes K0.3MoO3 and ″K0.28MoO″3, the stoichiometry K/Mo of which has been established using structural refinements as well as an electron probe microanalysis. The results show an independence of the wave number upon the alcaline concentration. We find that both samples have the same wave vector Q ≈(0, 0.75, 1 2 ) at low temperature, whereas in the quasi-one-dimensional band filling consideration and a Peierls scenario, the wave vector, for a K0.28MoO3 stoichiometry, is expected to be Q = (0, 0.75, 1 2 ) . The results are discussed in terms of either an additional non-stoichiometry or possible warped Fermi surface and bare phonon dispersion effects.

We report results of the electrical resistivity of the silver salt of 2,5-dimethyl-N,N'-dicyanoquinonediimine, (DMDCNQI)2Ag, at normal and applied pressure as well as of the thermoelectric power at ambient pressure. At room temperature, pressure induces a transition towards a more conductive state. The phase diagram of this compound includes the temperatures of resistivity minima and those of the metal-insulator transition. The first are shifted to lower temperature by pressure while the second are less sensitive to applied pressure. The present data together with previous results on ESR and X-ray diffuse scattering support the idea that the ground state is spin-Peierls. The phase diagram is discussed within the framework of a theory of competing interactions, elaborated for TMTSF and TMTTF salts.

A well defined metal-semiconductor has been observed at high pressure in K2Pt(CN)4Br0.33H2O by resistivity measurements up to 32 kbar. The transition temperature corresponds to a narrow peak in the logarithmic derivative ∂ 1n ϱ/∂ ( 1 T ) and its width is connected with the pressure enhanced 3-d coupling. The 32 kbar data are discussed in terms of a mean-field treatment of the Peierls transition (Horovitz, Gutfreund, Weger). This high pressure investigation suggest a possible suppression of the Peierls transition in KCP, above 70 kbar. Under the same conditions a superconductor, Tc ≅ 6Kcould possible exist.

We report a new phenomenon, namely, that upon cooling the valency of the rare-earth ion goes from one value to another at a characteristic temperature which upon further cooling returns to the original value at another characteristic temperature. We call this happening as the boomerang valence phenomenon which occurs because of our invention of a new order parameter.

We report a sharp discontinuity of the electrical resistivity, the thermoelectric power (TEP) and the ESR intensity of ethyl and methyldypropylamine TCNQ 2 around 212 K. In the high temperature phase (HT), the TEP tends to saturate to a value of ∼ - 70 μV K -1 indicating that the conducting electrons are strongly correlated and can be modelled as a strong coupling Hubbard model. In the low temperature phase (LT), in contrast with the normal behaviour of TCNQ salts, the conductivity reported here is larger than in the HT phase. The TEP is also larger in the LT phase. These results can be rationalized as coming from an increase of charge transfer ϱ as a consequence of the phase transition. Below T c the exchange interaction J is also stronger which indicates that this “inverse spin Peierls” transition involves a strong spin-phonon coupling.

We show that for a quasi 1-d metal the resistivity ϱ varies with temperature T as 1/sinh (ℏ ω /kBT), ℏω being the energy of the (external) 2kF phonon involved in the scattering process. The theory fits the observed ϱ vs. T of (TMTSF)2PF6 and other quasi 1-d metals below 60K, where lattice expansion, internal mode scattering and precursor effects of the Peierls transition can be neglected.

The mean field theory of the Peierls instability is extended to include the small momentum transfer interaction, which is shown to be a retarded interaction. The Peierls transition temperature is shown to depend significantly on the bare phonon frequency. A positive isotope shift parameter is predicted, with values in the range 0–0.5. It is also argued that the ratio of the zero temperature gap to the transition temperature is larger than the BCS value of 3.5.

We discuss the characteristic properties of the Spin-Peierls (SP) transition which allow one to distinguish experimentally between such a transition and the ordinary structural instability. It is shown that commensurability effects cause the strong dependence of the transition temperature T c on magnetic field H as well as nonlinear dependence of magnetization on H . They also suppress the phase fluctuations for the SP transition. It is shown also that dimensionless coupling constant of spin-phonon interaction which drives SP transition may be large enough only when the relevant phonon frequencies are extremely small already in a high-temperature phase.