Electron-lattice Interaction Research Articles

Structural features of nickel clad carbon fibers and determination of their thermophysical properties using pulsed radiation

It was considered the forming multilayer heat-resistant coatings that work under conditions of elevated temperatures and long-term oxidation. The issue of increasing the service life of the parts by strengthening their bulk and surface is considered. The issue of determining the level of the thermophysical properties is also considered. The thermophysical properties of carbonyl iron reinforced with carbon fibers (CF) pre-clad with nickel are investigated. Unclad and nickel clad carbon fibers were produced. The thermal conductivities of the samples are determined depending on the conditions of their production. The thermal conductivity characteristics of polymer composite materials based on CF with ceramic hollow microspheres and carbonyl iron from CF depending on the conditions of their production were determined. It is shown that heat transfer mechanisms related to the electron-lattice interaction can function in these systems. Heat transfer can occur by various transport mechanisms, such as collisions or diffusion. Nevertheless, the increase in thermal conductivity can be related to the electronic mechanism. The thermal conductivity of materials based on carbonyl iron with nickel-plated CF is 1.2 times higher compared to unclad CF, which is due to better adhesive interaction between the coated carbon fibers and iron was established.

Rise and Fall of Anderson Localization by Lattice Vibrations: A Time-Dependent Machine Learning Approach.

The intricate relationship between electrons and the crystal lattice is a linchpin in condensed matter, traditionally described by the Fröhlich model encompassing the lowest-order lattice-electron coupling. Recently developed quantum acoustics, emphasizing the wave nature of lattice vibrations, has enabled the exploration of previously uncharted territories of electron-lattice interaction not accessible with conventional tools such as perturbation theory. In this context, our agenda here is two-fold. First, we showcase the application of machine learning methods to categorize various interaction regimes within the subtle interplay of electrons and the dynamical lattice landscape. Second, we shed light on a nebulous region of electron dynamics identified by the machine learning approach and then attribute it to transient localization, where strong lattice vibrations result in a momentary Anderson prison for electronic wavepackets, which are later released by the evolution of the lattice. Overall, our research illuminates the spectrum of dynamics within the Fröhlich model, such as transient localization, which has been suggested as a pivotal factor contributing to the mysteries surrounding strange metals. Furthermore, this paves the way for utilizing time-dependent perspectives in machine learning techniques for designing materials with tailored electron-lattice properties.

Nanosecond Structural Dynamics during Electrical Melting of Charge Density Waves in 1T-TaS_{2}.

Electrical control of charge density waves has been of immense interest, as the strong underlying electron-lattice interactions potentially open new, efficient pathways for manipulating their ordering and, consequently, their electronic properties. However, the transition mechanisms are often unclear as electric field, current, carrier injection, heat, and strain can all contribute and play varying roles across length scales and timescales. Here, we provide insight on how electrical stimulation melts the room temperature charge density wave order in 1T-TaS_{2} by visualizing the atomic and mesoscopic structural dynamics from quasi-static to nanosecond pulsed melting. Using a newly developed ultrafast electron microscope setup with electrical stimulation, we reveal the order and strain dynamics during voltage pulses as short as 20ns. The order parameter dynamics across a range of pulse amplitudes and durations support a thermally driven mechanism even for fields as high as 19 kV cm^{-1}. In addition, time-resolved imaging reveals a heterogeneous, mesoscopic strain response across the flake, including MHz-scale acoustic resonances that emerge during sufficiently short pulsed excitation which may modulate the order. These results suggest that metallic charge density wave phases like studied here may be more robust to electronic switching pathways than insulating ones, motivating further investigations at higher fields and currents in this and other related systems.

Two distinct charge density waves in the quasi-one-dimensional metal Sr0.95NbO3.37 revealed by resonant soft X-ray scattering

The interplay of electron-electron and electron-lattice interactions plays an important role in determining exotic properties in strongly correlated electron systems. Of particular interest is quasi-one-dimensional SrNbOx metals, which are perovskite-related layered Carpy-Galy phases. Quasi-one-dimensional metals often exhibit a charge density wave (CDW) accompanied by lattice distortion; however, to date, the presence of a CDW in a quasi-one-dimensional metallic Carpy-Galy phase has not been detected. Here, we report the discovery of two distinct and simultaneous commensurate CDWs in Sr0.95NbO3.37 using resonant soft X-ray scattering (RSXS), namely, an electronic-(001) superlattice below ~ 200 K and an electronic-(002) Bragg peak. We also observe a non-electronic-(002) Bragg peak showing lattice distortion below ~ 150 K. Through the temperature dependence and resonance profile of these CDWs and the lattice distortion, as well as the relationship between the wavelength and charge density, these CDWs are determined to be Wigner crystals and Peierls-like instabilities, respectively. The electron‒electron interaction is strong and dominant even up to 350 K, and upon cooling, it drives the electron–lattice interaction. The correlation length of the electronic-(001) superlattice is surprisingly larger than that of the electronic-(002) Bragg peak, and the superlattice is highly anisotropic. Supported by theoretical calculations, the CDWs are determined by the charge anisotropy and redistribution between the O-2p and Nb-4d orbitals, and the strength of the electronic-(001) superlattice is within the strong coupling limit.

Fingerprints of the Jahn-Teller and superexchange physics in optical spectra of manganites

Transition metal oxides incorporating Jahn-Teller (JT) ions Mn3+ (3d 4) in manganites and Cu2+ (3d 9) in cuprates exhibit outstanding magnetic and electronic properties, including colossal magnetoresistance (CMR) and high-temperature superconductivity (HTSC). The physics of these compounds is associated with the orbitally-degenerate electronic states of JT ions, leading to the linear electron-lattice interaction, complemented by the entirely electronic superexchange (SE) interaction. Here, we discuss the fingerprints of the JT and SE physics in the temperature-dependent complex dielectric function spectra and multi-order Raman scattering spectra measured in a detwinned LaMnO3 crystal, which is a famous compound exhibiting cooperative JT effect, being also a progenitor of magnetic materials exhibiting CMR effect. In accordance with the obtained experimental evidence, the associated effective parameters characterizing the JT and SE physics in manganites are presented.

Effect of lattice distortion on spin admixture and quantum transport in organic devices with spin–orbit coupling

Abstract With an extended Su–Schrieffer–Heeger model and Green’s function method, the spin–orbit coupling (SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. The role of lattice distortion induced by the strong electron–lattice interaction in organics is clarified in contrast with a uniform chain. The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC, which is explained by the perturbation theory. The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes. A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes, where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained. Unlike the spin admixture, a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion. The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration, and hence the spin-flip transmission, instead of the spin admixture of eigenstates. This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.

Nonlinear charge and energy transport in anharmonic quasi-two-dimensional systems.

We study the localized states of an extra electron in an anisotropic quasi-two-dimensional system in which the electron-lattice interaction and the anharmonicity of the lattice vibrations are dominant in one direction. This model describes layers of polydiacetylene or other polymer chains, beta sheets of polypeptides, multilevel microstructures of conjugated polymers, and other low-dimensional systems. It is shown that for appropriate parameter values of the system an extra electron can excite a soliton-like mobile wave of the lattice deformation, within which it can get self-trapped. Such a bound state of an electron and the lattice deformation form a nonlinear two-component polaron-like entity, which can propagate with minimum of the energy dissipation. Our findings are based on the variational approach and the full numerical solution of the coupled system of nonlinear equations. These results suggest that the experimentally measured charge and energy transport over macroscopic distances in the above-mentioned systems can be provided by the soliton mechanism and thus have a potential impact on the theoretical background of the numerous applications of low-dimensional materials in nanoelectronics.

Temperature-driven journey of dark excitons to efficient photocatalytic water splitting in β-AsP.

Limited availability of photogenerated charge carriers in two-dimensional (2D) materials, due to high exciton binding energies, is a major bottleneck in achieving efficient photocatalytic water splitting (PWS). Strong excitonic effects in 2D materials demand precise attention to electron-electron correlation, electron-hole interaction and electron-phonon coupling simultaneously. In this work, we explore the temperature-dependent electronic and optical responses of an efficient photocatalyst, blue-AsP (β-AsP), by integrating electron-phonon coupling into state-of-the-art GW + BSE calculations. Interestingly, strong electron-lattice interaction at high temperature promotes photocatalytic water splitting with an increasing supply of long-lived dark excitons. This work presents an atypical observation contrary to the general assumption that only bright excitons enhance the PWS due to prominent absorption. Dark excitons, due to the low recombination rate, exhibit long-lived photogenerated electron-hole pairs with high exciton lifetime increasing with temperature up to ∼0.25 μs.

Antiferromagnetism and insulator-metal transition of alkali metal-loaded sodalite.

Alkali metal clusters with a single unpaired s-electron can be arranged three-dimensionally in a sodalite crystal by loading the guest alkali atoms. Na, K, and K-Rb alloy clusters are known to be Mott insulators and to exhibit antiferromagnetic ordering. The Néel temperature increases from about 50 K to about 100 K in this order. In this study, Li-Na alloy, Na-K alloy, and pure Rb samples were newly prepared and their magnetic, electrical conductivity, and optical properties were investigated, including those of previous samples. The Na-K alloy samples showed antiferromagnetic properties, which were intermediate between those of the Na and K samples. However, the Rb sample showed a non-magnetic metallic state. The shallower ionization potential in Rb is thought to cause an insulator-metal transition (Mott transition) due to weaker on-site Coulomb repulsion between electrons and larger electron transfer energy between neighboring clusters. On the other hand, the Li-Na alloy sample showed a non-magnetic insulating state. It is thought that the two electrons form a spin-singlet pair due to the strong electron-lattice interaction. In terms of electron correlations and polaron effects, the full picture of the element species dependence of the alkali metal-loaded sodalite is reviewed.

Large temperature coefficient of resistivity (TCR) of La0.67Ca0.33MnO3 polycrystalline ceramics improved by optimizing sintering temperatures

This work investigates fabrication of La0.67Ca0.33MnO3 (LCMO) polycrystalline ceramics using a facile sol–gel method at sintering temperatures (Ts) ranging from 1470 °C to 1540 °C and explores relationship between their electrical transport properties and Ts. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoemission spectroscopy were employed to characterize crystal structure, morphologies, element distributions, and Mn3+/Mn4+ ratio of the as-obtained LCMO ceramics. The influence of Ts on phase purity, microstructure, morphology, and electrical transport properties was also investigated. LCMO ceramics exhibit increased grain size and higher temperature coefficient of resistivity (TCR) at higher temperatures. An increase in Ts can reduce the strength of electron–lattice interactions and theoretical Curie temperature in LCMO ceramic samples, which can in turn optimize their electrical transport properties. Moreover, an increase in Ts enhances double-exchange (DE) effect to some extent. The DE effect further affects resistivity and metal–insulator transition temperature of material. Additionally, small-polaron hopping model and phenomenological percolation model were used to characterize electrical transport in metal–insulator transition region. The temperature at which TCR is maximum (265.78 K) and the largest TCR value (58.16 %) were achieved at a Ts of 1530 °C. By modulating the sintering temperature, we achieved LCMO ceramics with larger grains and enhanced electrical properties. This optimization renders materials suitable for highly sensitive infrared bolometer applications.

Relaxation processes among adiabatic potential energy surfaces of Tl+ and Au− centers in NaCl crystals

We investigated temperature dependencies of the temporal behaviors of luminescence bands attributed to the radiative transitions from adiabatic potential energy surfaces (APESs) of 1T1g, 3T2u+3Eu, 3T1g, and 3A1u of Tl+ and Au− centers in NaCl crystals. In addition to NaCl:Au−, a luminescence band with the sharp zero-phonon luminescence line was observed in NaCl:Tl+, a strong electron-lattice interaction system. A time-resolved study revealed that this luminescence band with the zero-phonon line in NaCl:Tl + exhibited the decay time of 4.3 ms at low temperatures attributed to the radiative transition from 3A1u APES. The characteristic temperature dependences of the decay time constant and luminescence intensity of the luminescence from the 3T1g and 3A1u APESs were discussed based on a configuration coordinate scheme. The intensities and decay time constants of luminescence bands caused by radiative transitions from the 1T1g, 3T2u+3Eu, 3T1g, and 3A1u APESs changed with temperature through thermally activated nonradiative transitions among APESs. The temperature dependencies of luminescence intensities and decay time constants were analyzed using rate equations that comprise radiative and nonradiative transitions from APESs and among APESs, respectively. The activation energies of APESs were estimated from the best-fit results. The characteristics of thermally activated processes among APESs are revealed in weak and strong electron-lattice interaction systems.

Transient responses of dielectrics during ultrashort pulsed laser irradiation using a generalized thermoelastic model considering temperature-dependent thermophysical properties

A novel model involving electron dynamics, electron-lattice interactions, and thermoelastic excitation for dielectrics exposed to ultrashort pulsed laser is proposed. The thermoelastic equations are modified based on the G-L generalized thermoelasticity and consider the temperature-dependent thermophysical properties. An axisymmetric problem of ultrashort pulsed laser irradiation on fused silica is presented. The fully-coupled equations are solved simultaneously using the finite element method to obtain the transient electron density, electron temperature, lattice temperature, and stresses. The evolution of transient responses and the effects of laser intensity, pulse duration, and temperature-dependent thermophysical properties are analyzed in detail. It was found that there are kinks in the distribution of transient responses, which is attributed to the rapid change of reflectivity. The axial stress has wave-like characteristics. The electron temperature is slightly lower than the lattice temperature after the thermal equilibrium is achieved. Maybe the temperature-dependence of lattice thermal conductivity could be neglected to reduce computational expenses.

Hidden Hexavalent Chromium Ions with Subtle Structural Evolution in Near-Infrared Phosphors.

Cr-doped inorganic materials are pivotal in developing near-infrared optical materials; however, multivalent Cr ions and their respective distribution in the materials remain ambiguous. Herein, a series of Li(Sc1-xInx)O2:Cr phosphors containing both Cr3+/Cr6+ ions are prepared. High-resolution synchrotron X-ray diffraction (XRD) reveals two similar phases in Li(Sc1-xInx)O2. Raman spectra further confirm distinct scattering patterns for the two end-member compositions, corroborating the findings from the synchrotron XRD analysis. Cr K-edge X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrate that most Cr ions in the as-prepared samples are Cr6+, while Cr3+ becomes dominant after washing with water. Moreover, the source and distribution of Cr3+ and Cr6+ ions in the as-prepared and washed samples are revealed through X-ray fluorescence and X-ray excited optical luminescence techniques, which indicate that Cr6+ ions aggregate within the sample, while Cr3+ ions are evenly distributed. Photoluminescence, decay curves, and line shape analyses are implemented to resolve the electron-lattice interactions, and the corresponding mechanisms are provided to explain the asymmetry between photoluminescence and photoluminescence excitation spectra. Overall, this study provides valuable insights into the distribution of low-concentration multivalence ions in solid-state materials and offers a deeper understanding of the approaches to precisely resolve the subtle changes in the crystal structure.

Exciton-induced electric dipole moment in organic ferromagnets

Based on an Anderson-like model including electron–lattice interaction and electron–electron (e–e) interactions, charge and spin properties of excitons in quasi-one-dimensional organic ferromagnets with spin radicals are investigated. The results demonstrate the appearance of an unusually large electric dipole moment in the magnetic molecule upon the formation of the exciton. The sign of the dipole moment depends on the spin of the excited electron relative to the magnetization of the spin radicals. The underlying mechanism is analysed based on the different charge distribution and lattice distortion in the two excitation modes with opposite spin. The origin is attributed to the preferred occupation on different domain walls of the exciton distortion for different spin-resolved excitonic levels. The experimental realization of the large dipole moment is discussed. Although the realization of a large dipole moment is impeded by the superposition state formed due to the degeneracy of two excitation modes, we propose an achievable route to break the symmetry and create controllable electric polarization by optical illumination. The dipole moment is robust even if the long-range e–e interaction is included. The effects of the system parameters, including the electron hopping between the main chain and the radicals and the e–e interaction, on the magnitude of the dipole moment are also discussed. This work indicates a novel way to realize organic multiferroic materials with controllable polarization, which can be induced by photon excitation.

Role of octahedral tilting and rotation in [formula omitted]MnO3 ([formula omitted]=La-Ho) perovskites: An orbital scenario

The octahedral tilting and rotation, i.e. GdFeO3-type distortion, in perovskite RMnO3 (R=rare-earth), are investigated with respect to the Jahn–Teller distortion within the unified orbital scenario. The evolution of orbital ordering and magnetism with the rare-earth R ions in perovskite RMnO3 are examined with an effective Hamiltonian based on the competitive mechanism of the electron–electron and electron-lattice interactions by the cluster self-consistent field approach. It is clearly found that the GdFeO3-type distortion enhances the magnitude of the Jahn–Teller distortion and suppresses the ferromagnetic coupling in ab-plane due to the decreasing of the superexchange interaction with Mn–O–Mn bond angle deviating from 180°, which are in good agreement with the experiments. Both the structural and magnetic properties can be explained in an orbital perspective consistently. Furthermore, our model is able to capture the experimental trends including both Jahn–Teller distortion and magnetic coupling for RMnO3 considering the combined effects of the GdFeO3-type distortion. Our results not only shed new light on the interplay of various degrees of freedom, but also unveil the stabilization mechanism of the crystal structure in perovskites.

Optically Induced Multistage Phase Transition in Coherent Phonon-Dominated a-GeTe.

Ultrafast photoexcitation can decouple the multilevel nonequilibrium dynamics of electron-lattice interactions, providing an ideal probe for dissecting photoinduced phase transition in solids. Here, real-time time-dependent density functional theory simulations combined with occupation-constrained DFT methods are employed to explore the nonadiabatic paths of optically excited a-GeTe. Results show that the short-wavelength ultrafast laser is capable of generating full-domain carrier excitation and repopulation, whereas the long-wavelength ultrafast laser favors the excitation of lone pair electrons in the antibonded state. Photodoping makes the double-valley potential energy surface shallower and allows the insertion of A1g coherent forces in the atomic pairs, by which the phase reversal of Ge and Te atoms in the ⟨001⟩ direction is activated with ultrafast suppression of the Peierls distortion. These findings have far-reaching implications regarding nonequilibrium phase engineering strategies based on phase-change materials.

Three-dimensional charge density wave in the dual heavy fermion system UPt2Si2

Heavy fermion liquids offer via their Kondo lattice diverse possibilities for exotic ground states. Using variable-temperature atomic pair distribution function analysis, we study the local atomic structure of the ``dual'' heavy fermion liquid $\mathrm{U}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$, which exhibits antiferromagnetism consistent with localized $5f$-electron states and transport properties characteristic to itinerant $5f$-``$spd$'' hybridized electron systems. We show that $\mathrm{U}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$ exhibits periodic lattice distortions (PLDs) involving both uranium and platinum atoms that are characteristic to three-dimensional charge density waves. The temperature evolution of the PLDs tracks that of the transport and magnetic properties, suggesting the presence of little-known $5f$-electron-lattice interactions. We argue that PLDs in heavy fermion liquids in general, and in particular in $\mathrm{U}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$, appear as new degrees of freedom that entangle competing electronic states and, as such, must be accounted for when their rich physics is considered.

Periodic Atomic Displacements and Visualization of the Electron-Lattice Interaction in the Cuprate

Traditionally, X-ray scattering techniques have been used to detect the breaking of the structural symmetry of the lattice, which accompanies a periodic displacement of the atoms associated with charge density wave (CDW) formation in the cuprate pseudogap states. Similarly, the Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM) has visualized the short-range CDW. However, local coupling of electrons to the lattice in the form of a short-range CDW has been a challenge to visualize, thus a link between these measurements has been missing. Here, we introduce a novel STM-based technique to visualize the local bond length variations obtained from topographic imaging with picometer precision. Application of this technique to the high-Tc cuprate superconductor Bi2Sr2CaCu2O8+{\delta} revealed a high-fidelity local lattice distortion of the BiO lattice as large as 2%. In addition, analysis of local breaking of rotational symmetry associated with the bond lengths reveals modulations around four-unit-cell periodicity in both B1 and E representations in the C4v group of the lattice, which coincides with the uni-directional d-symmetry CDW (dCDW) previously identified within the CuO2 planes, thus providing direct evidence of electron-lattice coupling in the pseudogap state and a link between the X-ray scattering and STM measurements. Overall, our results suggest that the periodic lattice displacements in E representations correspond to a locally-frozen version of the soft phonons identified by the X-ray scattering measurements, and a fluctuation of the bond length is reflected by the fluctuation of the dCDW formation near the quantum critical point.

Electron–lattice pair properties in chains with cubic interaction

In this paper, we investigate the one-electron propagation in a nonlinear chain with electron–lattice interaction. The model contains standard cubic nonlinear terms, and we introduce the coupling between the electron and the lattice through the hopping distribution. We solve the coupled equation set to electron and lattice and calculate the electronic position as a function of time. We provide a detailed investigation of the electron and lattice dynamics for a wide range of electron–lattice coupling intensities. Our results demonstrate that depending on the initial condition we consider and the intensity of the electron–lattice interaction, we can obtain (or not) an electron–phonon pair formation. Our results reveal that, depending on the initial velocity of the lattice and the degree of electron–lattice term, we can observe a repulsion between electron and lattice deformations.

Interfacial Hole-Charge-Transfer Dynamics in Organic Solar Cells: A Dynamic Viewpoint

The energy loss of hole-charge transfer in nonfullerene-acceptor (NFA) organic solar cells has been significantly reduced by minimizing their interfacial energy offset to near-zero and negative values. However, the physical mechanism of highly efficient hole-charge transfer in these conditions has not been fully addressed. In this work, we theoretically clarify that a moving hole charge along the polymer-donor and NFA interface, generated from the spontaneous dissociation of NFA molecular excited states, tends to transfer from NFA molecules to polymer-donor to keep moving, even their interfacial energy offset is chosen as a negative value. This dynamic viewpoint revises the conventional static viewpoint about the dependence of hole-charge transfer upon the interfacial energy offset. In addition, considering the polaron effect in organic molecules with a hole charge generated, we redefine the interfacial energy offset and further consider the effects of the NFA molecular electron-lattice interaction and lattice elastic constant on the hole-charge transfer.