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The dynamics of charge density waves (CDW) is described by the temporal changes of the amplitude and the phase of the complex CDW order parameter. Phasons (phase excitations) are acoustic-like low energy degrees of freedom and therefore govern low-frequency CDW response. Dynamics of the CDW dielectric glass transition strongly resembles scenario of freezing in supercooled liquids [1]. The well known CDW pinning is characterized by the resonant response at GHz frequencies. Screening by free carriers is tightly bound with the deformation of CDW and its relaxational dynamics giving the criterium for freezing at Tg [1]. CDW glassy phenomenology is completed with low-energy excitations, the peak in heat capacity (Cp/T3), long-time energy relaxation and aging found at low-T [2]. Relevant degrees of freedom in this new class of glass concern CDW superstructure on characteristic scales given by the size of the phase coherence length (lϕ~μm). As the lattice distortion associated with the CDW can be thought of as being a “frozen” phonon, we discuss its possible manifestations in relation with the phenomenology of Boson peak in glasses as freezing of incomplete softening of superstructural mode near glass transition temperature. The Boson peak frequency in CDW glass phenomenology can be seen as Ioffe-Regel limit for phason propagation, consistent with the pinning resonance (gap in the phason dispersion). Very well understood aspects of the microscopic picture in CDW systems dealing with pinning, screening and phasons as relevant excitations of defective superstructure (on mesoscopic, μm scales) and the parallels we draw with glass forming systems as defective soft structures (on nm scales) [3] might be of mutual interest for both fields.

The family of glasses includes nowadays numerous systems which are often very different from the classical glassformers, i.e. supercooled liquids. Even such exotic systems as charge density wave (CDW) superstructures occurring in quasi one-dimensional metals exhibit phenomena typical for glasses [1-3] including freezing of the primary relaxation (α) process at a finite temperature Tg [1], occurrence of the secondary (β) relaxation process below Tg [1], “Boson peak”- like [2] and power-law contributions [3] to the heat capacity. Disorder in CDW glasses is introduced on the level of superstructure through the pinning of CDW to crystalline defects which break CDW in domains determined by the coherence of the complex order parameter phase. Domain interaction is controlled by the screening of residual free carriers excited over CDW gap. Increase of the relaxation time at low temperatures follows the activated increase of resistivity which plays the role of viscosity. The glass transition occurs at a temperature Tg at which there is less then one free carrier per domain and the screening is no longer effective [1]. We have varied domain sizes in CDW system o-TaS3 over two orders of magnitude by proton irradiation which created additional defects. Dielectric spectroscopy on irradiated samples shows decrease of the amplitude and the microscopic relaxation time of α process, while the activation energy increases beyond the activation energy of resistivity, demonstrating increased cooperativity of the domains. Corresponding increase of Tg depends on the irradiation dose, and consequently on the domain size, in the activated manner. It follows closely the temperature dependence of free carrier density, which does not change with the irradiation, thus corroborating the freezing criterion for CDW glass. We demonstrate that Tg is closely related to the domain size in CDW glasses. As the microscopic model of CDW dynamics is well-established, our results might contribute to the understanding of the glass phenomenology in general.

Here we report on detailed studies of the photoexcited carrier and collective mode dynamics in prototype quasi-1D charge density wave (CDW) systems K0:3MoO3 and Rb0:3MoO3 focusing on their low temperature and low excitation range. We show that the order parameter relaxation dynamics are inconsistent with the Rothwarf– Taylor model describing the relaxation of the coupled quasi-particle and high frequency phonon system in a system with a narrow gap in the density of states. Therefore we propose an alternative model that accounts for the photoexcited carrier relaxation phenomena commonly observed in CDW systems.

We report on new method of measuring sample length, based on interferometric measurements. Motivation for exploring this technique is to study the coupling between charge density wave (CDW) and underlying crystal lattice. Several papers report the dilatation measurements on CDW systems which can be related to CDW transition [1], CDW hysteresis [2], as well as low Temperature glass transition [3]. Coupling with lattice is also evident from calorimetric measurements at glass transition temperature [4]. Our aim is to apply this method to other CDW systems as well as other systems with electronic superstructure.

Charge density wave (CDW) ground state consists of coherent superposition of bound electron-hole pairs from opposite sides of quasi one-dimensional (q1d) Fermi surface with 2kF common wavevector. The properties of new state at sufficiently low excitation energies can be described by spatio-temporal variations of corresponding order parameter. As CDW has zero net spin, majority of CDW models does not discriminate between different spin channels and, moreover, consider only the low lying excitations of CDW phase (phasons).

The quasi-onedimensional (Q1D) systems with charge density wave (CDW) ground state have been extensively investigated in the eighties until a “ concensus” on their properties has been reached, or maybe until the high temperature superconductors have been discovered. However, even 20 years later these systems do not end to surprise us that have continued the efforts to study them. Glass transition in the superstructure, random exchange Heisenberg antiferromegnetic chain (REHAC) behaviour of the susceptility, extreme doping sensitivity of the dielectric response and heat capacity, large thermal hysteresis in the dielectric response, large sensitivity of the low temperature conductivity on electric excitations which I will present are only some of many interesting phenomena that we have recently observed.

We show that the low temperature (T

We present the effects of doping on the relaxational dynamics and the specific heat (Cp) of the charge density wave (CDW) system o-TaS3. Isoelectronic substitution of Ta atoms with 0.2% of Nb suppresses the primary relaxation process responsible for the glass-like dielectric response of pure o-TaS3 [1], but affects only slightly the secondary process as well as the low energy excitation (LEE) contribution to Cp. As it is well established that doping destroys the long range CDW order, our results show that the primary relaxation process is mainly due to long range deformations of the CDW, which are prevented by doping, while the secondary process and the LEE contribution to Cp originate from local topological defects of the CDW still present in doped samples.

Low-frequency dielectric spectroscopy and thermally stimulated discharge measurements of charge-density wave (CDW) system K0.3MoO3 are presented. Below 80 K two distinct relaxational processes are observed, which freeze at finite temperatures bearing close resemblance to the phenomenology of the dielectric response of glasses. We compare our results to the case of o-TaS3 in which the glass transition on the level of CDW superstructure has been recently reported and discuss the possibility that it is a universal feature of CDW systems.

A detailed thermodynamical investigation of the quasi-one-dimensional sulphur-based organic salts (TMTTF)(2)PF6 and (TMTTF)(2)Br is presented in the temperature range from 30 mK to 7 K. In this part (part I), we consider the general aspects of the low-temperature specific heat of these materials in relationship with their ground states and we compare them with those previously measured for selenium members of the same family. All these compounds exhibit very similar thermodynamical behaviour, despite a variety of electronic ground states: spin-Peierls for (TMTTF)(2)PF6, commensurate antiferromagnetic spin modulation for (TMTTF)(2)Br, incommensurate spin-density wave for (TMTSF)(2)PF6 (TMTSF drop tetramethyltetraselenafulvalene). We show that the low-energy excitations which are predominant below 1 K have a similar character to that observed in glassy systems, at least on short timescales of measurements. The dynamical aspects of the non-equilibrium thermodynamics will be presented separately in the following part (part H).

This contribution is in continuation of our preceding publication (Lasjaunias J C, Brison J P, Monceau P, Staresinic D, Biljakovic K, Carcel C and Fabre J M 2002 J. Phys.: Condens. Matter 14 837) in which we have considered general aspects of the low-temperature thermodynamical properties of the quasi-one-dimensional organic salts based on sulphur donors with different ground states: (TMTTF)(2)PF6 in the spin-Peierls state and (TMTTF)(2)Br (TMTTF = tetramethyltetrathiafulvalene) with commensurate spin modulation. In this part, part 11, we present our results on the dynamical aspects related to the non-equilibrium phenomena measured below I K. The metastable states excited to slightly higher temperature (by only a few per cent of the starting T-0) relax very slowly to the heat bath environment, depending on the duration of the heat pumping. We compare the features observed in the relaxation rates in these two sulphur compounds with those measured for the incommensurate spin-density-wave compound (TMTSF)(2)PF6. We discuss the possible nature of the long-living low-energy excitations lying at the origin of this complex dynamical behaviour, in relation to their ground states.

We report on the power-law dependence on temperature of the magnetic susceptibility and the specific heat of the CDW (charge density wave) system o-TaS3. All the evidences are in favor of a typical REHAC (random exchange Heisenberg antiferromagnetic chain) behaviour [1], however in the diluted limit of spins s=1/2. We propose a consistent microscopic explanation of the corresponding elementary excitations within a new state formed below the glass transition demonstrated recently in this system [2].

We present experimental evidences for glass transitions in systems with modulated charge density wave (CDW) superstructure. Entire spectrum of observed phenomena shows close parallels with glass forming systems. Well understood microscopic mechanisms in CDW systems enable us to propose a scenario of the glass transition. It occurs on the level of CDW superstructure, when the elastic degrees of freedom are frozen by the increased Coulomb coupling between DW domains in the absence of screening. We can set a quantitative criterion for the temperature of the glass transition Tg: T at which there is less than one electron per domain. As similar phenomena have been observed in various charge and spin density systems, we suggest that the glass transition might be a generic feature of all DW systems.

We report on a study of the slow dynamics of the heat relaxation at very low temperature (T less than or equal to 1 K) in the nominally commensurate ground states of the sulfide compounds (TMTTF)(2)Br and (TMTTF)(2)PF6, commensurate SDW - or antiferromagnetic - and spin-Peierls, respectively. For both systems, the long-time dynamics at equilibrium shows a bimodal character, which can be analysed by slow and fast gaussian distributions g(logtau), separated by one decade in time, which can originate from defects of commensurability. [

We report on specific heat measurements of the quasi-one-dimensional organic salt (TMTSF)_2AsF_6 in its spin density wave state between 75 mK and 7 K. Similarly to (TMTSF)_2PF_6, we find discontinuities in the lattice contribution at 1.9 K and 3.5 K ascribed to sub-spin density wave phases. Time-dependent effects due to dynamics of low-energy excitations in metastable states occur only below 0.2 K which yields an activation energy for the equilibrium energy relaxation process of 0.34 K, 4-5 times smaller than found for (TMTSF)_2PF_6. Finally the reduction of the low-energy excitations contribution to the specific heat in comparison to PF_6 reveals an intermediate cubic-like regime between 0.25 and 0.5 K that we tentatively describe as the phason contribution of the incommensurate spin density wave modulation.

Quasi one- and two-dimensional conductors offer a wealth of new broken symmetry ground states such as charge/spin density waves, high temperature superconductors, (anti) ferroelectrics, colossal magnetoresistance systems etc. exhibiting fascinating collective phenomena. Low energy excitations of these electronic crystals, as topological defects in electronic superstructure (solitons, vortices and domain walls) and their interaction with underlying crystal, its boundaries and defects (impurities) largely determine their thermal, magnetic and transport properties. This workshop will deal with recent developments in understanding of static and dynamic properties of these collective states, particulary CDW. Special attention will be paid to the study of CDW at different spatio-temporal scales: high resolution x-ray spectroscopy, coherent diffraction, STM, femtosecond optical spectroscopy, optoelectric measurements, dielectric measurements and glassy relaxation, wavelet temporal analysis, meso- and nano-scale measurements.

The phase diagram of the Bechgaard and Fabre organic conductors is revisited. A special care is devoted to the commensurability effects associated with bond and site dimerization on the conducting organic chains which appear essential in the theoretical description of the observed phase diagram and of the physical behaviors associated with various phases. The bond dimerization effects are relevant in the paramagnetic insulating (MI) phase, in the (AF) phase with the tetramerized spin order, in the spin-Peierls (SP) phase with lattice tetramerization added to the (AF) spin order while the bond/site charge dimerization is relevant in the (CO) phase. The relevance of dimerizations is experimentally observed by the enhancement of the dimerization of distances between the adjacent organic molecules in the MI, AF and SP phases and by the apparition of the homogeneous shift of the counter ion lattice along the direction of the molecular chains in the CO phase. This ferroelectric shift is driven by the the charge disproportiation between adjacent organic molecular sites. In contrast to that, the dimerization of the intermolecular distances and/or the homogeneous shift of the counter ions is absent in the superconducting phase, strongly indicating that the latter is stable only when the dimerization is irrelevant. Those observations are traditionally related to the behavior of the dominant fluctuations in the purely 1d weak coupling model with forward and backward scatterings g2 and g1 of comparable magnitude and an Umklapp scattering g3 induced by dimerization, which is relatively small. The “ phase diagram” of the 1d model is carefully reconsidered with the emphasis on the behavior in the region of (g2 - g1/2) ≈ -| g3 |. For (g2 - g1/2) close above -| g3 | the Mott gap Δ ρ is finite but extremely small. For larger (g2 - g1/2) it remains small due to the relative smallness of | g3 |. The dominant 1d fluctuations below Δ ρ are of the AF type (spin tetramerization). It is emphasized that in the range -| g3

The spectral properties of quasi-one dimensional metals at the higher energies of the order of plasmon and/or bandwidth energy are investigated by applying the standard co-called G0W0 approximation in the calculation of the dressed electron Green's function with the screened long-range three-dimensional Coulomb interaction obtained within the random phase approximation (RPA). First we assume a strictly one-dimensional electron band due to a finite transfer integral along the chains, and in the second step we extend the consideration to a more realistic case of electron band with a finite interchain hopping. As long as there is no interchain hopping the spectral function doesn't have low-energy quasi-particle, but contains broad structure with the width of the order of plasmon energy. Such spectral properties are in qualitative agreement with ARPES spectra of Bechgaard salts.