Search

(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

Fundamental electronic principles underlying all transition metal compounds are the symmetry and filling of the $d$-electron orbitals and the influence of this filling on structural configurations and responses. Here we use a sensitive local structural technique, x-ray atomic pair distribution function analysis, to reveal the presence of fluctuating local-structural distortions at high temperature of one such compound, \cis . We show that this hitherto overlooked fluctuating symmetry lowering is electronic in origin and will significantly modify the energy-level spectrum and electronic and magnetic properties. The explanation is a local, fluctuating, orbital-degeneracy-lifted state. The natural extension of our result would be that this phenomenon is likely to be widespread amongst diverse classes of partially filled nominally degenerate d-electron systems, with potentially broad implications for our understanding of their properties., 10 pages 3 figures

Recently the structural transition in Na2Ti3Cl8 at 200 K with the formation of triangular Ti3 clusters was studied by ab-initio calculations in PRL 124, 167203 (2020). It was concluded on the basis of the DFT+U results that the usual band effects are not sufficient to explain this transition. The authors then invoked magnetic mechanisms, including complicated factors such as biquadratic and ring exchanges. We point out that this overcomplicated description is unnecessary, and that the formation of trimers, or breathing kagome lattice in Na2Ti3Cl8, and in many other systems, has very simple, almost trivial explanation basing on the orbital-driven Peierls transition.

We demonstrate an experimental approach to determining the excited-state interatomic forces using femtosecond x-ray pulses from an x-ray free-electron laser. We determine experimentally the excited-state interatomic forces that connect photoexcited carriers to the nonequilibrium lattice dynamics in the prototypical Peierls-distorted material, bismuth. The forces are obtained by a constrained least-squares fit of a pairwise interatomic force model to the excited-state phonon dispersion relation as measured by the time- and momentum-resolved x-ray diffuse scattering. We find that photoexcited carriers weaken predominantly the nearest-neighbor forces, which drives the measured softening of the transverse acoustic modes throughout the Brillouin zone as well as the zone-center ${A}_{1g}$ optical mode. This demonstrates a bond-selective approach to measuring electron-phonon coupling relevant to a broad range of photoinduced phase transitions and transient light-driven states in quantum materials.

The spinel-structure CuIr$_{2}$S$_{4}$ compound displays a rather unusual orbitally-driven three-dimensional Peierls-like insulator-metal transition. The low-T symmetry-broken insulating state is especially interesting due to the existence of a metastable irradiation-induced disordered weakly conducting state. Here we study intense femtosecond optical pulse irradiation effects by means of the all-optical ultrafast multi-pulse time-resolved spectroscopy. We show that the structural coherence of the low-T broken symmetry state is strongly suppressed on a sub-picosecond timescale above a threshold excitation fluence resulting in a structurally inhomogeneous transient state which persists for several-tens of picoseconds before reverting to the low-T disordered weakly conducting state. The electronic order shows a transient gap filling at a significantly lower fluence threshold. The data suggest that the photoinduced-transition dynamics to the high-T metallic phase is governed by first-order-transition nucleation kinetics that prevents the complete ultrafast structural transition even when the absorbed energy significantly exceeds the equilibrium enthalpy difference to the high-T metallic phase. In contrast, the dynamically-decoupled electronic order is transiently suppressed on a sub-picosecond timescale rather independently due to a photoinduced Mott transition., arXiv admin note: substantial text overlap with arXiv:2005.02207

A correlation is established between the theories of superconductivity based on the concept of charge density waves (CDW) and the translation invariant (TI) bipolaron theory. It is shown that CDW are originated from TI-bipolaron states in the pseudogap phase due to Kohn anomaly and form a pair density wave (PDW) for wave vectors corresponding to nesting. Emerging in the pseudogap phase, CDW coexist with superconductivity at temperatures below that of superconducting transition while their wave amplitudes decrease as a Bose condensate is formed from TI-bipolarons, vanishing at zero temperature., Slightly edited and enhanced version. Published in Front. Phys. 7 pages, 1 figure

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.

We show by advanced electronic structure calculations that ${\mathrm{NbO}}_{2}$ essentially is a Peierls-type material. After simulating the rutile as well as the body-centered tetragonal phase with the Bethe-Salpeter equation, we are able to reproduce the experimental values for the electronic properties without adding correlations. Our calculation includes only excitonic corrections and no further interactions. The principal indirect gap is between $N$ and $\mathrm{\ensuremath{\Gamma}}$ and is found to be 0.98 eV, the direct gap at the $\mathrm{\ensuremath{\Gamma}}$ point amounts to 1.35 eV. We found the rutile structure to be anisotropic, with nesting vectors in the Fermi surfaces in the $\mathrm{\ensuremath{\Gamma}}MAZ$ and $\mathrm{\ensuremath{\Gamma}}XRZ$ planes.

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.

International audience; Neutral modes related to spontaneous broken symmetries at the onset of a pattern-forming instability can strongly modify the nature of secondary instabilities of the pattern. In particular these neutral modes can change the order of the secondary transition making it first order or subcritical in the language of bifurcation theory. We first discuss this phenomenon in the context of the drift bifurcation from stationary to traveling patterns. We then consider patterns that undergo a spatial period-doubling bifurcation like the Peierls transition in solid state physics.; Je rappelle comment une expérience réalisée par Yves Couder et son groupe a motivé des travaux théoriques qui ont montré que les modes de phase d'une structure cellulaire engendrée par instabilité peuvent affecter la nature des instabilités secondaires de cette structure, à savoir, le caractère propagatif ou non de l'instabilité secondaire et sa sous-criticalité. Je discute ensuite la sous-criticalité résultant du couplage avec les modes de phase sur d'autres exemples tels que la transition de Peierls en physique de la matière condensée.

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 long-standing problem surrounding the metal-insulator transition of VO${}_{2}$ is the relative role of Mott and Peierls instabilities. Here, the authors investigate the change in electronic and crystal structures of nanostructured VO${}_{2}$ films, where the balance between the two instabilities is controlled as a function of thickness. $I\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ photoemission spectroscopy reveals that VO${}_{2}$ in the thin limit exhibits a Mott insulating nature without the V-V dimerization characteristic of bulk VO${}_{2}$, owing to the dominance of the Mott instability over the Peierls one.

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.

The spin-Peierls transition at ${T}_{\mathrm{SP}}$ of spin-$\frac{1}{2}$ chains with isotropic exchange interactions has previously been modeled as correlated for $Tg{T}_{\mathrm{SP}}$ and mean field for $Tl{T}_{\mathrm{SP}}$. We use correlated states throughout in the ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model with antiferromagnetic exchange ${J}_{1}$ and ${J}_{2}=\ensuremath{\alpha}{J}_{1}$ between first and second neighbors, respectively, and variable frustration $0\ensuremath{\le}\ensuremath{\alpha}\ensuremath{\le}0.50$. The thermodynamic limit is reached at high $T$ by exact diagonalization of short chains and at low $T$ by density matrix renormalization group calculations of progressively longer chains. In contrast to mean field results, correlated states of 1D models with linear spin-phonon coupling and a harmonic adiabatic lattice provide an internally consistent description in which the parameter ${T}_{\mathrm{SP}}$ yields both the stiffness and the lattice dimerization $\ensuremath{\delta}(T)$. The relation between ${T}_{\mathrm{SP}}$ and $\mathrm{\ensuremath{\Delta}}(\ensuremath{\delta},\ensuremath{\alpha})$, the $T=0$ gap induced by dimerization, depends strongly on $\ensuremath{\alpha}$ and deviates from the BCS gap relation that holds in uncorrelated spin chains. Correlated states account quantitatively for the magnetic susceptibility of TTF-${\mathrm{CuS}}_{4}{\mathrm{C}}_{4}{({\mathrm{CF}}_{3})}_{4}$ crystals (${J}_{1}=79\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, $\ensuremath{\alpha}=0$, ${T}_{\mathrm{SP}}=12\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and ${\mathrm{CuGeO}}_{3}$ crystals (${J}_{1}=160\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, $\ensuremath{\alpha}=0.35$, ${T}_{\mathrm{SP}}=14\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). The same parameters describe the specific heat anomaly of ${\mathrm{CuGeO}}_{3}$ and inelastic neutron scattering. Modeling the spin-Peierls transition with correlated states exploits the fact that $\ensuremath{\delta}(0)$ limits the range of spin correlations at $T=0$ while $Tg0$ limits the range at $\ensuremath{\delta}=0$.

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.

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 introduce variational wave functions to evaluate the ground-state properties of spin-phonon coupled systems described by the Su-Schrieffer-Heeger model. Quantum spins and phonons are treated on equal footing within a Monte Carlo sampling, and different regimes are investigated. We show that the proposed variational Ansatz yields good agreement with previous density-matrix renormalization group results in one dimension and is able to accurately describe the spin-Peierls transition. This variational approach is neither constrained by the magnetoelastic-coupling strength nor by the dimensionality of the systems considered, thus allowing future investigations in more general cases, which are relevant to spin-liquid and topological phases in two spatial dimensions., 7 pages, 5 figures

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

The local structure of NaTiSi$_{2}$O$_{6}$ is examined across its Ti-dimerization orbital-assisted Peierls transition at 210 K. An atomic pair distribution function approach evidences local symmetry breaking preexisting far above the transition. The analysis unravels that on warming the dimers evolve into a short range orbital degeneracy lifted (ODL) state of dual orbital character, persisting up to at least 490 K. The ODL state is correlated over the length scale spanning $\sim$6 sites of the Ti zigzag chains. Results imply that the ODL phenomenology extends to strongly correlated electron systems., Comment: 7 pages, 5 figures

International audience; Lattice dynamics of low-dimensional BaVS3 is reported across the metal-insulator Peierls transition occurring at TP=69 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density-functional theory calculations. The nondetection of a Kohn anomaly points to a unique situation of an order-disorder Peierls instability with a quasielastic critical scattering which has been fully characterized. These observations are discussed in the scope of a Peierls instability dominated by strong electron-phonon coupling and/or nonadiabatic effects.

We have studied the electronic structure of ${\mathrm{BaCoO}}_{3}$ using soft x-ray absorption spectroscopy at the Co ${L}_{2,3}$ and O $K$ edges, magnetic circular dichroism at the Co ${L}_{2,3}$ edges, and valence band hard x-ray photoelectron spectroscopy. The quantitative analysis of the spectra established that the Co ions are in the formal low-spin tetravalent $3{d}^{5}$ state and that the system is a negative charge transfer Mott insulator. The spin-orbit coupling also plays an important role for the magnetism of the system. At the same time, a trigonal crystal field is present with sufficient strength to bring the $3{d}^{5}$ ion away from the ${J}_{\mathrm{eff}}=1/2$ state. The sign of this crystal field is such that the ${a}_{1g}$ orbital is doubly occupied, explaining the absence of a Peierls transition in this system, which consists of chains of face-sharing ${\mathrm{CoO}}_{6}$ octahedra. Moreover, with one hole residing in ${e}_{g}^{\ensuremath{\pi}}$, the presence of an orbital moment and strong magnetocrystalline anisotropy can be understood. Yet we also infer that crystal fields with lower symmetry must be present to reproduce the measured orbital moment quantitatively, thereby suggesting the possibility for orbital ordering to occur in ${\mathrm{BaCoO}}_{3}$.

We predict a mechanism of spontaneous stabilization of a uniaxial density wave in a two-dimensional metal with an isotropic Fermi surface in the presence of external magnetic field. The topological transformation of a closed Fermi surface into an open one decreases the electron band energy due to delocalization of electrons initially localized by magnetic field, additionally affected by the magnetic breakdown effect. The driving mechanism of such reconstruction is a periodic potential due to the self-consistently formed electron density wave. It is accompanied with quantum oscillations periodic in inverse magnetic field, similar to the standard de Haas - van Alphen effect, due to Landau level filling. The phase transition appears as a quantum one at T=0, provided the relevant coupling constant is above the critical one. This critical value rapidly decreases, and finally saturates toward zero on the scale of tens of Tesla. Thus, a strong enough magnetic field can induce the density wave in the system in which it was absent in zero field., Comment: 12 pages, 4 figures

We show that, assisted by the Peierls transition of lattice, as a quasi-one dimensional (Q1D) tight binding system, a Mobius molecular device can behave as a simple topological insulator. With the Peierls phase transition to form a domain wall, the solitonary zero modes exist as the ground state of this electron-phonon hybrid system, which is protected by the Z2 topology of the Mobius strip. The robustness of the ground state prevents these degenerate zero modes from their energy spectrum splitting caused by any perturbation.

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.

In materials with nearly commensurate band filling the electron liquid may spontaneously separate into components with distinct properties, yielding complex intra- and interunit cell ordering patterns and a reduced dimensionality. Polarization-dependent angle-resolved photoemission data with submicron spatial resolution demonstrate such an electronic self-organization in NbSe3, a compound considered to be a paradigm of charge order. The new data indicate the emergence of a novel order, and reveal the one-dimensional (1D) physics hidden in a material which naively could be considered the most three dimensional of all columnar chalcogenides. The 1D physics is evidenced by a new selection rule—in two polarizations we observe two strikingly different dispersions each closely resembling apparently contradicting results of previous studies of this material., The work at Lausanne and Geneva is supported by the Swiss NSF. M.A.V. acknowledges financial support from Spanish MICIN Postdoctoral Mobility Program. S.P. acknowledges C’NANO Ile-de-France, DIM NanoK, for the support of the Nanospecs project. Work in Spain was supported by a MINECO (Grants FIS2015-64886-C5-4-P and CTQ2015-64579-C3-3-P), Generalitat de Catalunya (2017SGR1506 and 2017SGR1289), and XRQTC. E.C. acknowledges support from MINECO through the Severo Ochoa Centers of Excellence Program under Grant No. SEV-2015-0496. ICN2 is funded by the CERCA Program/ Generalitat de Catalunya, and supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV- 2017-0706). P.A. acknowledges support from the Maria de Maeztu Units of Excellence Program under Grant MDM- 2017-0767. S.C. gratefully acknowledges the Becas Chile program (CONICYT PAI/INDUSTRIA 72090772) for a doctoral grant at the Universitat de Barcelona. Synchrotron SOLEIL is supported by the Centre National de la Recherche Scientifique (CNRS) and the Commissariat à l’Energie Atomique et aux energies Alternatives (CEA).

${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ is considered a promising excitonic insulator (EI) candidate, in which the EI state is due to Coulomb interaction between electrons and holes. In ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$, the role of phonons is significant since the EI transition is accompanied by an orthorhombic-to-monoclinic structural transition at ${T}_{\mathrm{s}}=328\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Our inelastic x-ray scattering measurements reveal that the transverse acoustic mode exhibits strong softening just above ${T}_{\mathrm{s}}$. Furthermore, the transverse optical mode exhibits linewidth broadening caused by strong electron--optical-phonon coupling above ${T}_{\mathrm{s}}$. Density functional theory calculations indicate that the coupled optical modes arise due to the vibration of Ta ions. Consequently, in the monoclinic phase, the coupled optical modes are ``frozen'' such that Ta and Se approach each other, forming atomic-displacement-type electric dipoles that are obviously different from a Peierls transition or Jahn--Teller distortion. The characteristic of electronic toroidal moment formation by the antiferroelectric arrangements of the electric dipoles forms the common feature between ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ and $1T\ensuremath{-}\mathrm{TiS}{\mathrm{e}}_{2}$.

Nanoelectromechanical systems (NEMS) that operate in the megahertz (MHz) regime allow energy transducibility between different physical domains. For example, they convert optical or electrical signals into mechanical motions and vice versa. This coupling of different physical quantities leads to frequency-tunable NEMS resonators via electromechanical non-linearities. NEMS platforms with single- or low-degrees of freedom have been employed to demonstrate quantum-like effects, such as mode cooling, mechanically induced transparency, Rabi oscillation, two-mode squeezing and phonon lasing. Periodic arrays of NEMS resonators with architected unit cells enable fundamental studies of lattice-based solid-state phenomena, such as bandgaps, energy transport, non-linear dynamics and localization, and topological properties, directly transferrable to on-chip devices. Here we describe one-dimensional, non-linear, nanoelectromechanical lattices (NEML) with active control of the frequency band dispersion in the radio-frequency domain (10–30 MHz). The design of our systems is inspired by NEMS-based phonon waveguides and includes the voltage-induced frequency tuning of the individual resonators. Our NEMLs consist of a periodic arrangement of mechanically coupled, free-standing nanomembranes with circular clamped boundaries. This design forms a flexural phononic crystal with a well-defined bandgap, 1.8 MHz wide. The application of a d.c. gate voltage creates voltage-dependent on-site potentials, which can significantly shift the frequency bands of the device. Additionally, a dynamic modulation of the voltage triggers non-linear effects, which induce the formation of a phononic bandgap in the acoustic branch, analogous to Peierls transition in condensed matter. The gating approach employed here makes the devices more compact than recently proposed systems, whose tunability mostly relies on materials’ compliance and mechanical non-linearities.

We study a one-dimensional system of strongly correlated bosons on a dynamical lattice. To this end, we extend the standard Bose-Hubbard Hamiltonian to include extra degrees of freedom on the bonds of the lattice. We show that this minimal model exhibits phenomena reminiscent of fermion-phonon models. In particular, we discover a bosonic analog of the Peierls transition, where the translational symmetry of the underlying lattice is spontaneously broken. This provides a dynamical mechanism to obtain a topological insulator in the presence of interactions, analogous to the Su-Schrieffer-Heeger model for electrons. We characterize the phase diagram numerically, showing different types of bond order waves and topological solitons. Finally, we study the possibility of implementing the model using atomic systems.

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.

The finite-temperature entanglement entropy for an alternating spin-1/2 chain with multi-spin interactions is investigated by means of Green’s function theory combined with Jordan-Wigner transformation, to identify the spin-Peierls (SP) transition. It is found that the two-site thermal entanglement entropy is a useful tool to characterize theSPtransition. In addition, the competition between multi-spin interaction and Peierls-dimerization plays a central role in the critical phenomenon of the system.

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 extend the continuous-time interaction-expansion quantum Monte Carlo method with respect to measuring observables for fermion-boson lattice models. Using generating functionals, we express expectation values involving boson operators, which are not directly accessible because simulations are done in terms of a purely fermionic action, as integrals over fermionic correlation functions. We also demonstrate that certain observables can be inferred directly from the vertex distribution, and present efficient estimators for the total energy and the phonon propagator of the Holstein model. Furthermore, we generalize the covariance estimator of the fidelity susceptibility, an unbiased diagnostic for phase transitions, to the case of retarded interactions. The new estimators are applied to half-filled spinless and spinful Holstein models in one dimension. The observed renormalization of the phonon mode across the Peierls transition in the spinless model suggests a soft-mode transition in the adiabatic regime. The critical point is associated with a minimum in the phonon kinetic energy and a maximum in the fidelity susceptibility., 12 pages, 4 figures, 1 table; final version

We use the density matrix renormalization group method to investigate the role of longitudinal quantized phonons on the Peierls transition in the spin-Peierls model. For both the $XY$ and Heisenberg spin-Peierls model we show that the staggered phonon order parameter scales as $\sqrt{\ensuremath{\lambda}}$ (and the dimerized bond order scales as $\ensuremath{\lambda}$) as $\ensuremath{\lambda}\ensuremath{\rightarrow}0$ (where $\ensuremath{\lambda}$ is the electron-phonon interaction). This result is true for both linear and cyclic chains. Thus, we conclude that the Peierls transition occurs at $\ensuremath{\lambda}=0$ in these models. Moreover, for the $XY$ spin-Peierls model we show that the quantum predictions for the bond order follow the classical prediction as a function of inverse chain size for small $\ensuremath{\lambda}$. We therefore conclude that the zero $\ensuremath{\lambda}$ phase transition is of the mean-field type.

The density matrix renormalization group method is used to investigate the spin-Peierls transition for Heisenberg spins coupled to quantized phonons. We use a phonon spectrum that interpolates between a gapped, dispersionless (Einstein) limit to a gapless, dispersive (Debye) limit. A variety of theoretical probes are used to determine the quantum phase transition, including energy gap crossing, a finite size scaling analysis, bond order auto-correlation functions, and bipartite quantum entanglement. All these probes indicate that in the antiadiabatic phonon limit a quantum phase transition of the Berezinskii-Kosterlitz-Thouless type is observed at a non-zero spin-phonon coupling, $g_{\text c}$. An extrapolation from the Einstein limit to the Debye limit is accompanied by an increase in $g_{\text c}$ for a fixed optical ($q=\pi $) phonon gap. We therefore conclude that the dimerized ground state is more unstable with respect to Debye phonons, with the introduction of phonon dispersion renormalizing the effective spin-lattice coupling for the Peierls-active mode. We also show that the staggered spin-spin and phonon displacement order parameters are unreliable means of determining the transition., Comment: To be published in Phys. Rev. B

A study of electron spin resonance in uncompensated Ge:As semiconductor samples in the vicinity of the insulator-metal second-order phase transiti on reveals that the interaction of spins localized at As atoms brings about a distortion of the crystal lattice and enhances the localization. This effect occurs in the range of electron concentrations n = 3 × 1017—3.7 × 1017 cm-3, just below the critical point of the phase transition. The effect is explained in the context of a model considering the spin-Peierls transition in the random impurity sublattice of the semiconductor, and its features, as compared to other known materials where the spin-Peierls transition is observed, are understood.

We investigate the ground-state properties of polyacene in terms of an extended Peierls-Hubbard Hamiltonian with particular emphasis on its structural instability of two types: double bonds in a cis pattern and those in a trans pattern. The two Peierls-distorted states are degenerate in their energetics but quite distinct in their optics. The trans configuration is easily photoconverted into the cis one, whereas an opposite transition, if any, is hardly completed. Domain-wall (soliton) excitations play an important role in any photoinduced phase transitions, but charged and neutral ones behave quite differently.

We have numerically studied the phonon softening in a triangular lattice system with Su–Schrieffer–Heeger's (SSH) type interaction and with a three-quarter-filled electronic band. When the temperature is lowered, the simultaneous softening of multiple phonon modes is observed at a critical temperature. These softened modes have momenta parallel to the vectors connecting neighboring vertices of the hexagonal structure of the Fermi surface, being irrelevant to nesting vectors. Therefore, this phenomenon that occurs when the temperature is lowered is not a conventional Peierls transition. It is found that the Fermi surface composed of straight lines is a necessary condition for the simultaneous phonon softening. Multi-mode states are realized below the critical temperature. However, all of the softened modes are not necessarily condensed at the lowest free-energy state.

Giant nonlinear conduction in the charge ordered organic conductor θ ‐ ( BEDT ‐ TTF ) 2 MM ′ ( SCN ) 4 ( M = Cs , Rb; M ′ = Co , Zn) is analyzed in relation to the current-induced suppression of the charge ordered state characterized by a wave vector of q 2 = ( 0 k 1 2 ) . On the basis of a theory of the nonequilibrium Peierls transition, the energy gap is calculated as a function of current density J ext , which is found to depend weakly on temperature in an intermediate temperature range. This justifies the evaluation of the charge-order energy gap Δ from the nonlinear resistivity ρ assuming ρ ∝ exp [ Δ ( J ext ) / k B T ] , and Δ ( J ext ) is found to be consistent with the calculation. We compare the present results with nonequilibrium superconducting states induced by excess quasiparticles, and discuss a mechanism of current-induced suppression of the charge ordering in the title compound.

The 2D Peierls transition in an anisotropic triangular lattice is studied from the view point of phonon softening. The model is obtained by introducing a coupling in one of the diagonal directions to the isotropic square lattice, for which the multimode Peierls phase, involving not only the nesting vector component but also other Fourier components of distortion with wave vectors parallel to the nesting vector, is predicted. The results indicate that the multimode type Peierls transition can be expected as far as the diagonal coupling is weak compared to the nearest neighbor coupling in the square lattice.

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.

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.

Energy band theory is introduced as an extension of the molecular orbital theory, and applied to organic conductors. From this, we can discuss the Fermi surface of organic conductors.

Electron spin resonance and electron–proton double resonance (Overhauser shift method) are used for the comparison of proton radiation damaged and as-grown (fluoranthene) 2 PF 6 single crystals. Chemical modification and various consequences of the nonuniform distribution of radiation induced defects in this quasi-one-dimensional organic conductor with defect dependent Peierls transition are worked out.

Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K2Cr8O16, which exhibits a temperature-dependent (T-dependent) paramagnetic-to-ferromagnetic- metal transition at T-C = 180 K and transforms into a ferromagnetic insulator below T-MI = 95 K. We observe clear T-dependent dynamic valence (charge) fluctuations from above T-C to T-MI, which effectively get pinned to an average nominal valence of Cr+3.75 (Cr4+:Cr3+ states in a 3:1 ratio) in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0) similar to 3.5(k(B)T(MI)) similar to 35 meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U similar to 4 eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr) and the half-metallic ferromagnetism in the t(2g) up-spin band favor a low-energy Peierls metal-insulator transition.

One-dimensional (1D) solids exhibit a number of striking electronic structures including charge-density wave (CDW) and spin-density wave (SDW). Also, the Peierls theorem states that at zero temperature, a 1D system predicted by simple band theory to be a metal will spontaneously dimerize and open a finite fundamental bandgap, while at higher temperatures, it will assume the equidistant geometry with zero bandgap (a Peierls transition). We computationally study these unique electronic structures and transition in polyyne and all-trans polyacetylene using finite-temperature generalizations of ab initio spin-unrestricted Hartree–Fock (UHF) and spin-restricted coupled-cluster doubles (CCD) theories, extending upon previous work [He et al., J. Chem. Phys. 140, 024702 (2014)] that is based on spin-restricted Hartree–Fock (RHF) and second-order many-body perturbation (MP2) theories. Unlike RHF, UHF can predict SDW as well as CDW and metallic states, and unlike MP2, CCD does not diverge even if the underlying RHF reference wave function is metallic. UHF predicts a gapped SDW state with no dimerization at low temperatures, which gradually becomes metallic as the temperature is raised. CCD, meanwhile, confirms that electron correlation lowers the Peierls transition temperature. Furthermore, we show that the results from all theories for both polymers are subject to a unified interpretation in terms of the UHF solutions to the Hubbard–Peierls model using different values of the electron-electron interaction strength, U/t, in its Hamiltonian. The CCD wave function is shown to encompass the form of the exact solution of the Tomonaga–Luttinger model and is thus expected to describe accurately the electronic structure of Luttinger liquids.