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(Quasi-)one-dimensional systems exhibit various fascinating properties such as Luttinger liquid behavior, Peierls transition, novel topological phases, and the accommodation of unique quasiparticles (e.g., spinon, holon, and soliton, etc.). Here we study molybdenum blue bronze A0.3MoO3 (A = K, Rb), a canonical quasi-one-dimensional charge-density-wave material, using laser-based angle-resolved photoemission spectroscopy. Our experiment suggests that the normal phase of A0.3MoO3 is a prototypical Luttinger liquid, from which the charge-density-wave emerges with decreasing temperature. Prominently, we observe strong renormalizations of band dispersions, which is recognized as the spectral function of Holstein polaron derived from band-selective electron-phonon coupling in the system. We argue that the strong electron-phonon coupling plays a dominant role in electronic properties and the charge-density-wave transition in blue bronzes. Our results not only reconcile the long-standing heavy debates on the electronic properties of blue bronzes but also provide a rare platform to study novel composite quasiparticles in Luttinger liquid materials., 19 pages, 4 figures, accepted by Nature Communications

It is shown that in orthorhombic TaS3 with quenching defects, when the temperature changes in the region below the Peierls transition temperature T < TP, forced diffusion of defects arises due to their strong interaction with the charge density wave (CDW). The relationships between the concentration of quenching defects, n, the threshold field of the onset of CDW sliding, ET, and the defect-induced shift of TP are determined: ET∝ n and ΔTP∝ n. This set of laws corresponds to the case when quenching defects positions are correlated with the CDW. The ordinary (without thermocycling) diffusion of quenching defects was detected at T ≈ 300 K, its diffusion coefficient and the height of the energy barrier were estimated. This made it possible to clarify the most probable nature of the defects. These are interstitial sulfur impurities introduced during quenching into the van der Waals gap between the chains and partially ordered at T < TP due to interaction with the CDW. This ordering significantly lowers the height of the energy barrier of forced diffusion in comparison with ordinary diffusion when the spatial configuration of the CDW changes during thermocycling. This leads to the appearance of anomalously high low-temperature forced mobility of correlated impurities.

The 1D wire TaS3 exhibits metallic behavior at room temperature but changes into a semiconductor below the Peierls transition temperature (Tp), near 210 K. Using the 3ω method, we measured the thermal conductivity κ of TaS3 as a function of temperature. Electrons dominate the heat conduction of a metal. The Wiedemann–Franz law states that the thermal conductivity κ of a metal is proportional to the electrical conductivity σ with a proportional coefficient of L0, known as the Lorenz number—that is, κ=σLoT. Our characterization of the thermal conductivity of metallic TaS3 reveals that, at a given temperature T, the thermal conductivity κ is much higher than the value estimated in the Wiedemann–Franz (W-F) law. The thermal conductivity of metallic TaS3 was approximately 12 times larger than predicted by W-F law, implying L=12L0. This result implies the possibility of an existing heat conduction path that the Sommerfeld theory cannot account for.

Effects of the collective motion (sliding) of a charge density wave in the TbTe3 quasi-two-dimensional conductor have been studied in a wide temperature interval. Immediately after cooling to temperatures below the Peierls transition temperature TCDW = 336 K, the threshold field Et of sliding initiation of the charge density wave has a nearly linear temperature dependence. The aging of samples at a fixed temperature T0 < TCDW for several hours significantly modifies the sliding of the charge density wave. The threshold field increases significantly and the temperature dependence of Et becomes nonmonotonic, demonstrating a large maximum at T = T0. The observed effect is attributed to the aging-induced formation of an ordered structure (lattice) of defects of the charge density wave and to change in the pinning regime at the melting of this structure.

The 1D wire TaS3 exhibits metallic behavior at room temperature but changes into a semiconductor below the Peierls transition temperature (Tp), near 210 K. Using the 3ω method, we measured the thermal conductivity κ of TaS3 as a function of temperature. Electrons dominate the heat conduction of a metal. The Wiedemann–Franz law states that the thermal conductivity κ of a metal is proportional to the electrical conductivity σ with a proportional coefficient of L0, known as the Lorenz number—that is, κ=σLoT. Our characterization of the thermal conductivity of metallic TaS3 reveals that, at a given temperature T, the thermal conductivity κ is much higher than the value estimated in the Wiedemann–Franz (W-F) law. The thermal conductivity of metallic TaS3 was approximately 12 times larger than predicted by W-F law, implying L=12L0. This result implies the possibility of an existing heat conduction path that the Sommerfeld theory cannot account for.

NbSe3 and monoclinic-TaS3 (m-TaS3) are quasi-1D metals containing three different types of chains and undergoing two different charge density wave Peierls transitions at ${T}_{{\mathrm{P}}_{1}}$ and ${T}_{{\mathrm{P}}_{2}}$ associated with type III and type I chains, respectively. The nature of these transitions is discussed on the basis of first-principles DFT calculation of their Fermi surface (FS) and electron–hole response function. Because of the stronger inter-chain interactions, the FS and electron–hole response function are considerably more complex for NbSe3 than m-TaS3; however a common scenario can be put forward to rationalize the results. The intra-chain inter-band nesting processes dominate the strongest response for both type I and type III chains of the two compounds. Two well-defined maxima of the electron–hole response for NbSe3 are found with the (0a*, 0c*) and (1/2a*, 1/2c*) transverse components at ${T}_{{\mathrm{P}}_{1}}$ and ${T}_{{\mathrm{P}}_{2}}$, respectively, whereas the second maximum is not observed for m-TaS3 at ${T}_{{\mathrm{P}}_{2}}$. Analysis of the different inter-chain coupling mechanisms leads to the conclusion that FS nesting effects are only relevant to set the transverse a* components in NbSe3. The strongest inter-chain Coulomb coupling mechanism must be taken into account for the transverse coupling along c* in NbSe3 and along both a* and c* for m-TaS3. Phonon spectrum calculations reveal the formation of a giant 2kF Kohn anomaly for m-TaS3. All these results support a weak coupling scenario for the Peierls transition of transition metal trichalcogenides., This work was supported by Spanish MINECO (the Severo Ochoa Centers of Excellence Program under Grants SEV 2017-0706 and FUNFUTURE CEX2019-000917-S), Span ish MICIU, AEI and EU FEDER (Grants No. PGC2018- 096955-B-C43 and No. PGC2018-096955-B-C44), General itat de Catalunya (Grant No. 2017SGR1506 and the CERCA Programme), and the European Union MaX Center of Excel lence (EU-H2020 Grant No. 824143). Phonons computational resources have been provided by the supercomputing facil ities of the Universit´e catholique de Louvain (CISM/UCL) and the Consortium des Équipements de Calcul Intensif en F´ed´eration Wallonie Bruxelles (CÉCI) funded by the Fond de la Recherche Scientifique de Belgique (FRS-FNRS) under convention 2.5020.11 and by the Walloon Region.

The voltage dependences of conductivity, $\ensuremath{\sigma}(V)$, of the monoclinic phase of ${\mathrm{NbS}}_{3}$ are reported. The extremely high coherence of the room-temperature charge density wave (CDW) allows its synchronization by a rf field up to ${T}_{\mathrm{P}1}\ensuremath{\approx}365\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the temperature of the Peierls transition, and above it by about 10 K. The ratio of nonlinear current, ${I}_{\mathrm{nl}}=I\ensuremath{-}V\ensuremath{\sigma}(0)$, to the fundamental frequency of the CDW sliding, ${f}_{\mathrm{f}}$, falls as T increases across ${T}_{\mathrm{P}1}$. This result is considered in terms of spontaneous phase slippage near ${T}_{\mathrm{P}1}$, which could give both single-particle and collective contributions to linear conductivity. The two contributions are considered, and the former is found to dominate. The temperature-frequency dependence of ${I}_{\mathrm{nl}}/{f}_{f}$ is consistent with the model of thermally activated phase slippage.

We have studied the magnetic, magnetotransport, and galvanomagnetic properties of ${\mathrm{TmNiC}}_{2}$. We find that the antiferromagnetic and field induced metamagnetic and ferromagnetic orderings do not suppress the charge density wave. The persistence of Fermi surface pockets, open as a result of imperfect nesting accompanying the Peierls transition, results in an electronic carriers mobility of the order of $4\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }{\mathrm{cm}}^{2}\text{ }{\mathrm{V}}^{\ensuremath{-}1}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ in ferromagnetic state, without any signatures for a significant deterioration of nesting properties. This is independently evidenced by high, nonsaturating linear magnetoresistance reaching 440% at $T=2\text{ }\text{ }\mathrm{K}$ and an analysis of the Hall conductivity. We thus demonstrate that, the coexistence of charge density wave and magnetism provides an alternative route to maintain high electronic mobility in the magnetically ordered state.

Soft-phonon modes of an undistorted phase encode a material’s preference for symmetry lowering. However, the evidence is sparse for the relationship between an unstable phonon wavevector’s reciprocal and the number of formula units in the stable distorted phase. This “1/q*-criterion” holds great potential for the first-principles design of materials, especially in low-dimension. We validate the approach on the Q1D organometallic materials space containing 1199 ring–metal units and identify candidates that are stable in undistorted (1 unit), Peierls (2 units), charge density wave (3–5 units), or long wave (>5 units) phases. We highlight materials exhibiting gap-opening as well as an uncommon gap-closing Peierls transition and discuss an example case stabilized as a charge density wave insulator. We present the data generated for this study through an interactive publicly accessible Big Data analytics platform (https://moldis.tifrh.res.in/data/rmq1d) facilitating limitless and seamless data-mining explorations.

The Peierls instability toward a charge density wave is a canonical example of phonon-driven strongly correlated physics and is intimately related to topological quantum matter and exotic superconductivity. We propose a method to realize an analogous photon-mediated Peierls transition, using a system of one-dimensional tubes of interacting Bose or Fermi atoms trapped inside a multimode confocal cavity. Pumping the cavity transversely engineers a cavity-mediated metal--to--insulator transition in the atomic system. For strongly interacting bosons in the Tonks-Girardeau limit, this transition can be understood (through fermionization) as being the Peierls instability. We extend the calculation to finite values of the interaction strength and derive analytic expressions for both the cavity field and mass gap. They display nontrivial power law dependence on the dimensionless matter-light coupling., Comment: 6 pages, 2 figures; supplement of 4 pages; published version

In the present Letter, a numerical study of the dynamic properties of one-dimensional (1D) incommensurate charge density wave (CDW) compound in the presence of free carriers (not affected by the Peierls transition) is carried out. The results obtained showed that the CDW sliding state is very sensitive to this local effect. The CDW depinning threshold field, excess current normalized and amplitude of Narrow-Band-Noise (NBN) are affected by these single particle’s excitations. This latter can be viewed as a screening effect of the applied electrical field by free carriers which relax in order to reduce the CDW polarization and generate a homogeneous system response.

Using time- and angle-resolved photoemission spectroscopy, we investigate the photoexcited electron dynamics in a prototypical charge density wave (CDW) material, Rb0.3MoO3. We observe a pronounced slow relaxation component within the CDW-gap energies. This anomalously slow dynamics is independent of the wave number, and cannot be explained by the presence of impurities. We propose that phase-coherent domains are temporarily established after a transient closure of the CDW gap, and that the intragap excitations are attributed to relaxation of the domain boundaries.

A charge density wave (CDW) ground state is observed in polycrystalline Cu2Se below 125 K, which corresponds to an energy gap of 40.9 meV and an electron-phonon coupling constant of 0.6. Due to the polycrystalline structure, the Peierls transition process has been expanded to a wide temperature range from 90 K to 160 K. The Hall carrier concentration shows a continuous decrease from 2.1 × 1020 to 1.6 × 1020 cm−3 in the temperature range from 160 K to 90 K, while almost unchanged above 160 K and below 90 K. After entering the CDW ground state, a wave-like fluctuation was observed in the I-V curve near 50 K, which exhibits a periodic negative differential resistivity in an applied electric field due to the current. We also investigated the doping effect of Zn, Ni, and Te on the CDW ground state. Both Zn and Ni doped Cu2Se show a CDW character with increased energy gap and electron-phonon coupling constant, but no notable Peierls transition was observed in Te doped Cu2Se. Similar wave-like I-V curve was also seen in Cu1.98Zn0.02Se near 40 K. The regular fluctuation in the dc I-V curve was not magnetic field sensitive, but temperature and sample size sensitive.

The uniaxial strain of quasi-one-dimensional conductor whiskers of orthorhombic TaS3 at a strain higher than e c ~ 0.8% leads to a sharp increase in the coherence of the properties of a charge density wave (CDW), which manifests itself in its motion in fields higher than threshold field E t . During uniaxial elongation, TaS3 is shown to exhibit the following unusual properties even in weak fields: Peierls transition temperature T P depends nonmonotonically on e, one-dimensional fluctuations weaken near T P , and the coherence length of a charge density increases at T < T P . Investigations in fields higher than E t show that the ultracoherent properties of CDW exist in a wide temperature range and are retained when temperature increases up to T P . These properties of CDW make it possible to observe a sharp increase in E t near T P and an almost jumplike increase in E t at T < 90 K. The increase in E t at T P is explained by a decrease in the coherence volume of CDW because of a fluctuational suppression of the Peierls gap.

We show that the charge density wave (CDW) ground state below the Peierls transition temperature, $T_{CDW}$, of rare-earth tritellurides is not at its equilibrium value, but depends on the time where the system was kept at a fixed temperature below $T_{CDW}$. This ergodicity breaking is revealed by the increase of the threshold electric field for CDW sliding which depends exponentially on time. We tentatively explain this behavior by the reorganization of the oligomeric (Te$_x$)$^{2-}$ sequence forming the CDW modulation., Comment: 10 pages, 5 figures, accepted in PRB

We review salient structural and electronic features associated with the concomitant Peierls–charge density wave (CDW) instabilities observed in most one-dimensional (1D) inorganic and organic electronic conductors. First of all, the genesis of these concepts is placed in an historical perspective. We then present basic experimental facts supporting the general description of these 1D electron–phonon coupled systems developed in the 1970s. In this framework we shall consider in particular the role of 1D fluctuations on both lattice and electronic degrees of freedom, and of the inter-chain Coulomb coupling between CDWs in stabilizing in 3D the Peierls transition at finite temperature. We also clarify, in relation with experimental findings, the various conditions of adiabaticity of the electron–phonon coupling. Finally we illustrate by recent structural measurements the pioneering work of Jacques Friedel on CDW elasticity and plasticity and CDW pinning to defects through the appearance of Friedel oscillations.

Scanning tunneling microscopy, low-energy electron diffraction, and helium atom scattering show a transition to a dimerizationlike reconstruction in the one-dimensional atomic chains on Bi(114) at low temperatures. One-dimensional metals are generally unstable against such a Peierls-like distortion, but neither the shape nor the spin texture of the Bi(114) Fermi contour favors the transition: Although the Fermi contour is one dimensional and thus perfectly nested, the very short nesting vector $2{k}_{F}$ is inconsistent with the periodicity of the distortion. Moreover, the nesting occurs between two Fermi contour branches of opposite spin, which is also expected to prevent the formation of a Peierls phase. Indeed, angle-resolved photoemission spectroscopy does not reveal any change in the electronic structure near the Fermi energy around the phase transition. On the other hand, distinct changes at higher binding energies are found to accompany the structural phase transition. This suggests that the transition of a strong-coupling type and that it is driven by phonon entropy rather than electronic entropy. This picture is supported by the observed short correlation length of the pairing distortion, the second-order-like character of the phase transition, and pronounced differences between the surface phonon spectra of the high- and low-temperature phases.

Diminishing in the concentration of quenching defects during thermocycling of orthorhombic TaS$_3$ samples in the temperature range below the Peierls transition temperature $T, Comment: LaTeX, 6 pages, 5 figures

Ultrafast electron diffraction is employed for study of structural dynamics at surfaces in the time domain. Experiments are performed in a pump probe setup with fs-laser excitation and subsequent probing through diffraction of a fs electron pulse at a temporal resolution of 350 fs. The system of interest is one atomic layer of indium atoms on a Si(111) surface: Through self-assembly In atomic wires and form which exhibits a Peierls-like, insulator to metal phase transition which can be driven non-thermally through a femtosecond-laser pulse. Through the transient intensity of the diffraction spots we observe the lifting of the Peierls transition and melting of a charge density wave in only 700 fs, heating of the surface in 6 ps, and formation of a metastable and supercooled phase which exists for nanoseconds.

The magnetoresistance of a TbTe3 two-dimensional conductor with a charge-density wave (CDW) has been measured in a wide temperature range and in magnetic fields of up to 17 T. At temperatures well below the Peierls transition temperature and in high magnetic fields, the magnetoresistance exhibits a linear dependence on the magnetic field caused by the scattering of normal charge carriers by “hot” spots of the Fermi surface. In the sliding CDW regime in low magnetic fields, a qualitative change in the magnetoresistance has been observed associated with the strong scattering of carriers by the sliding CDW.

Impurities and defects are known to affect the properties of the charge density wave (CDW) state but the influence of impurities on the density of states inside the Peierls gap remains largely unexplored. Here we present an experimental study of the effect of indium impurities on photoconduction spectra of CDW compound orthorhombic TaS$_3$. We use the temperature diffusion method to introduce indium into a sample from preliminary attached In contacts. The concentration of In after 23 hours of diffusion is found to be nonuniform and strongly dependent on the distance to the contacts. The diffusion affects the spectral range 0.15-0.25 eV, increasing the photoconduction amplitude linearly with diffusion time. The optical gap value obtained from the measurements is $2\Delta = 0.25$ eV and the tail of states below $2\Delta$ is associated with the impurities in agreement with the T\"{u}tt\"{o}-Zawadowski theory. Diffusion-induced modification of current-voltage characteristics and decrease of the Peierls temperature are also observed. Neither changes in photoconduction spectra nor in the Peierls transition temperature of the control sample with Au contacts are found., Comment: 6 pages, 6 figures. To be published in Physica B

We show that the isotropic conductivity in the normal state of rare-earth tritelluride RTe3 compounds is broken by the occurrence of the unidirectional charge density wave (CDW) in the (a,c) plane below the Peierls transition temperature. In contrast with quasi-one-dimensional systems, the resistivity anomaly associated with the CDW transition is strong in the direction perpendicular to the CDW wave vector Q (a-axis) and very weak in the CDW wave vector Q direction (c-axis). We qualitatively explain this result by calculating the electrical conductivity for the electron dispersion with momentum-dependent CDW gap as determined by angle-resolved photoemission spectroscopy (ARPES). Nonlinear transport properties in TbTe3 and GdTe3 have been studied along different crystallographic orientations. The pronounced effect of collective CDW motion is observed along c-axis and is absent completely in the perpendicular direction demonstrating the unidirectional character of the CDW. The threshold electric field for CDW sliding is linearly temperature dependent in a wide range of temperature.

Physical properties for the late-lanthanide-based $R{\mathrm{NiC}}_{2}$ ($R=\mathrm{Dy}$, Ho, Er, and Tm) ternary compounds are reported. All the compounds show antiferromagnetic ground state with the N\'eel temperature ranging from 3.4 K for ${\mathrm{HoNiC}}_{2}$ to 8.5 K for ${\mathrm{ErNiC}}_{2}$. The results of the transport and galvanomagnetic properties confirm a charge density wave state at and above room temperature with transition temperatures ${T}_{\mathrm{CDW}}=284$, 335, 366, and 394 K for ${\mathrm{DyNiC}}_{2}$, ${\mathrm{HoNiC}}_{2}$, ${\mathrm{ErNiC}}_{2}$, and ${\mathrm{TmNiC}}_{2}$, respectively. The Peierls temperature ${T}_{\mathrm{CDW}}$ scales linearly with the unit cell volume. A similar linear dependence has been observed for the temperature of the lock-in transition ${T}_{1}$ as well. Beyond the intersection point of the trend lines, the lock-in transition is no longer observed. In this Rapid Communication we demonstrate an extended phase diagram for the $R{\mathrm{NiC}}_{2}$ family.

In this work, we present a numerical simulation study of the dynamic properties of the charge density waves (CDW) in one-dimensional system. We present firstly, the results obtained within the classical model where the CDW is assimilated to a rigid particle. While this model explains qualitatively the CDW conductivity field dependence, a smooth discordance with the experimental results is observed. We present also the results obtained in the context of the deformable model where the CDW is considered as a continuum medium in interaction with the randomly distributed impurities in the lattice. The results obtained within this mode are in good concordance with the experimental ones which showing that the internal degrees of freedom play a capital role in the CDW dynamic properties.

We summarize structural instabilities exhibited by the one dimensional (1D) (arene)2X family of organic conductors in relation with their electronic and magnetic properties. With a charge transfer of one electron to each anion X these salts exhibit a quarter-filled (hole) conduction band located on the donor stacks. Compounds built with donors such as fluorenthene and perylene derivatives and anions X such PF6 or AsF6 exhibit a high temperature (TP~170K) conventional Peierls transition which is announced by a sizeable regime of 1D 2kF charge density wave fluctuations (kF is the Fermi wave vector of the 1D electron gas located on Per stacks). Surprisingly, and probably because of the presence of a multi-sheet warped Fermi surface, the Peierls transition is considerably reduced in the perylene series α-(Per)2[M(mnt)2] where X is the dithiolate molecule with M=Au, Cu, Co and Fe. A special attention is devoted in this paper to physical properties of α-(Per)2[M(mnt)2] salts which with M=Pt, Pd and Ni incorporate segregated S=1/2 1D antiferromagnetic (AF) dithiolate stacks with 1D metallic Per stacks. We analyse conjointly the structural and magnetic properties of these salts in relation with the 1D spin-Peierls (SP) instability located on the dithiolate stacks. We show that the SP instability of the Pd and Ni derivatives occurs in the classical (adiabatic limit) while the SP instability of the Pt derivative occurs in the quantum (anti-adiabatic limit). Furthermore we show that in the Pd and Ni derivatives frustrated 1st neighbour direct and 2nd neighbour indirect (through a fine tuning with the mediated 2kF RKKY coupling interaction on Per stacks) AF interactions add their contribution to the SP instability to open a singlet-triplet gap. Our analysis of the data show unambiguously that magnetic α-(Per)2[M(mnt)2] salts are a typical realization of the physics predicted for two chain 1D Kondo lattices.

Detailed structural and magnetotransport properties of monophosphate tungsten bronze ${\text{K}}_{x}({\text{PO}}_{2}){}_{4}({\text{WO}}_{3}){}_{8}$ single crystals are reported. Both galvanomagnetic and thermal properties are shown to be consistent with a charge density wave electronic transition due to hidden nesting of the quasi-1D portion of the Fermi surface. We also observe the enhancement of electronic anisotropy due to reconstruction of the Fermi surface at the Peierls transition. The resistivity presents a thermal hysteresis suggesting a first-order nature characteristic of a strong-coupling scenario. However, other measurements such as the change of carrier density demonstrate a second-order Peierls scenario with weak-coupling features. We suggest that the structural transition driven by the residual strain in the K-P-O environment is responsible for the resistivity hysteresis and modifies the Fermi surface which then helps the rise to the second-order Peierls instability.

We report synthesis of quasi-one-dimensional conductor NbS 3 , TEM studies and transport properties ofthe prepared samples. The grown NbS 3 whiskers are Peierls conductors known as phase II with thetransitions at T P1 ¼365 K and T P2 ¼150 K. CDW1 is stable and not so sensitive to growth conditions. Itcan slide and be synchronized by the external microwave irradiation up to 16 GHz. CDW2 stronglydepends on growth conditions. Nevertheless, it also shows sliding and synchronization.& 2012 Elsevier B.V. All rights reserved. 1. IntroductionNbS 3 , phase II, is standing out for its extremely high Peierlstransition temperature, T P ¼ 330–355 K [1]. Studies of this phasewere complicated because of the difficulties with its synthesis.The number of NbS 3 polytypes is not quite clear yet. The mostreproducible in synthesis is phase I (triclinic), high-ohmic at all T;it does not show clear evidence for CDW transport. Phase II ismonoclinic with 8Nb chains per unit cell and shows approximatetrimerisation below T

Department of Chemistry, University of California, One Shields Avenue, Davis, CA 95616, USAReceived 20 July 2011, revised 16 September 2011, accepted 26 September 2011Published online 28 December 2011Dedicated to Thomas Frauenheim on the occasion of his 60th birthdayKeywords charge-density wave, electron transport, entropy, in adsorption, nanowire, Peierls transition, Si(111) surface

The concepts spin density wave, charge density wave, and Peierls transition are reviewed with reference to various theoretical models and to their relevance for the interpretation of experimental data.

We report the effects of electric field induced deformations of quasi one-dimensional conductors with charge-density wave (CDW). The most pronounced sort of deformation is torsional strain (TS). The TS is found to comprise two contributions. The features of the 1st—the larger one—are threshold hysteretic dependence on electric field and high relaxation time τ : For o-TaS 3 τ ∼10 −2 s at T =80 K and falls as exp(900 K/ T ) with increasing T . The 2nd contribution is linear in electric field and does not drop with frequency increase. The amplitude of this contribution falls abruptly with T approaching the Peierls transition temperature T P from below. Similar features of TS are demonstrated for other CDW compounds: (TaSe 4 ) 2 I, K 0.3 MoO 3 and NbS 3 type II, for which T P ≈360 K. We attribute the 1st and the 2nd contributions to large (hysteretic) and small (near-equilibrium) CDW deformations, respectively, likely—shear at the surface. The TS is observed also above T P : For TaS 3 and (TaSe 4 ) 2 I typical torsional amplitude is 10 −1 °/V in the resonance regimes, corresponding to the piezomodulus ∼10 −9 m/V. A separate study of TS was performed at room temperature with AFM technique. Apart from this (‘intrinsic’) effect, we observe electrostatic contribution to the TS. In contrast to the intrinsic response, the electrostatic one is proportional to the potential either over the sample, or over an additional electrode (‘gate’) placed nearby, but not to the difference of potentials between the sample ends. It is typically 2 orders of magnitude less. The intrinsic TS reveals a new electromechanical effect at room temperature, presumably associated with the excitations of the pinned mode of the CDW fluctuations. Its observation opens prospects for application of quasi one-dimensional conductors as micro- and nano-actuators. Basing on the electrostatic-induced TS we propose prototypes of electrometers and a technique for measurements of work function changes. Using a cryogenic transmission electronic microscope we observe also flexural deformation of TaS 3 in the double-clamped mode, visible both in resonant and static modes.

The effect of a magnetic field on the energy gap of the charge density wave (CDW) in NbSe3 near the temperature T p2 of the lower Peierls transition has been investigated using interlayer tunneling spectroscopy. It has been shown that the magnetic field increases the energy gap and can even induce it at temperatures higher than T p2 by 15–20 K. As the field strength increases, the peak amplitude of the gap singularity of the tunneling spectrum first increases, reaches its maximum at 20–30 T, and then decreases. The increase in the gap peak amplitude is attributed to the field-induced improvement of the condition of the CDW nesting, while the decrease in the amplitude in high fields, to the breakdown of the ground state caused by its Zeeman splitting.

The Fermi surface topology of the layered superconducting charge density wave compound ZrTe3is investigated by angle resolved photoelectron spectroscopy and density functional theory. The Fermi surface is dominated by bands originating from two perpendicular systems of quasi one-dimensional chains. Nesting and opening of a pseudogap at temperatures as high as 250 K are signatures of a Peierls transition in one of these chains. The nesting properties are also studied for high pressure simulated crystal structure.