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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.

A complex character of the mechanism of thermal phase transformations from the insulating phase to the metallic phase has been revealed in thin V2O3 films. The insulator–metal phase transition in V2O3 is shown to consist of two stages: the hysteresis-less temperature-extended electron Mott transition extended in temperature and the stepwise structural Peierls transition with temperature hysteresis. The features of the insulator–metal phase transition revealed for V2O3 are discussed. These features are analyzed on the base of their comparison with characteristic features of analogous phase transition in VO2 films.

The origin of the charge density wave in TaTe4 is discussed on the basis of a first-principles density functional theory analysis of the Fermi surface, electron-hole response function, phonon band structure of the average structure, and structural optimization of the modulated phase. Analysis of the band structure and Fermi surface of the average structure clearly proves that despite the presence of TaTe4 chains in the crystal structure, TaTe4 is in fact a 3D material as far as the electronic structure near the Fermi level is concerned. A Fermi surface nesting mechanism is dismissed as the origin of the 2a × 2a × 3c structural modulation. The optimized 2a × 2a × 3c structure, which is found to be the more stable modulation in agreement with the experimental observations, can be obtained directly from a soft-phonon mode computed for the undistorted structure. Our results suggest that the driving force for the distortion is the maximization of Ta-Ta metal-metal bonding subject to inducing the minimum bonding decrease in the Te sublattice., This paper was supported by Spanish MINECO (the Severo Ochoa Centers of Excellence Program under Grants No. SEV-2017-0706 and No. FUNFUTURE CEX2019- 000917-S), Spanish MICIU, AEI, and EU FEDER (Grants No. PGC2018-096955-B-C43 and No. PGC2018-096955-BC44), Generalitat de Catalunya (Grant No. 2017SGR1506 and the CERCA Programme), and the European Union MaX Center of Excellence (EU-H2020 Grant No. 824143). Computational resources have been provided partially by the supercomputing facilities of the Université Catholique de Louvain (CISM/UCL) and the Consortium des Équipements de Calcul Intensif en Fédération Wallonie Bruxelles (CÉCI) funded by the Fond de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under Convention No. 2.5020.11 and by the Walloon Region.

Revealing the bonding and time-evolving atomic dynamics in functional materials with complex lattice structures can update the fundamental knowledge on rich physics therein, and also help to manipulate the material properties as desired. As the most prototypical chalcogenide phase change material, Ge_{2}Sb_{2}Te_{5} has been widely used in optical data storage and nonvolatile electric memory due to the fast switching speed and the low energy consumption. However, the basic understanding of the structural dynamics on the atomic scale is still not clear. Using femtosecond electron diffraction, structure factor calculation, and time-dependent density-functional theory molecular dynamic simulation, we reveal the photoinduced ultrafast transition of the local correlated structure in the averaged rocksalt phase of Ge_{2}Sb_{2}Te_{5}. The randomly oriented Peierls distortion among unit cells in the averaged rocksalt phase of Ge_{2}Sb_{2}Te_{5} is termed as local correlated structures. The ultrafast suppression of the local Peierls distortions in the individual unit cell gives rise to a local structure change from the rhombohedral to the cubic geometry within ∼0.3 ps. In addition, the impact of the carrier relaxation and the large number of vacancies to the ultrafast structural response is quantified and discussed. Our Letter provides new microscopic insights into contributions of the local correlated structure to the transient structural and optical responses in phase change materials. Moreover, we stress the significance of femtosecond electron diffraction in revealing the local correlated structure in the subunit cell and the link between the local correlated structure and physical properties in functional materials with complex microstructures.

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.

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

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.

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.

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.

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.

For broad nanoscale applications, it is crucial to implement more functional properties, especially those ferroic orders, into two-dimensional materials. Here GdI$_3$ is theoretically identified as a honeycomb antiferromagnet with large $4f$ magnetic moment. The intercalation of metal atoms can dope electrons into Gd's $5d$-orbitals, which alters its magnetic state and lead to Peierls transition. Due to the strong electron-phonon coupling, the Peierls transition induces prominent ferroelasticity, making it a multiferroic system. The strain from undirectional stretching can be self-relaxed via resizing of triple ferroelastic domains, which can protect the magnet aganist mechnical breaking in flexible applications., Comment: 6 pages, 4 figures

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

$VO_2$ undergoes the insulator-metal transition (IMT) and monoclinic-rutile structural phase transition (SPT) near $67^oC$. The IMT switching has many applications. However, there is an unresolved issue whether the IMT is a Mott transition or a Peierls transition. This complication is caused by metal and insulator coexistence, which is an inherent property of the IMT region. Thus, the acquired data in the IMT region are averaged over the two phases in many experiments. We overcome the issue by probing the electronic state of the monoclinic structure and by introducing a model that accounts for the coexisting phases. We reveal the Mott IMT in the non-distorted monoclinic nanodomain between $55-63^oC$, and the distortion-assisted SPT above $60^oC$., 18 pages, 4 main figures, 5 supporting figures