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Due to the high structural flexibility and controllable thermal expansion, cubic double ReO3-type negative thermal expansion (NTE) fluorides provide a solution for solving the prominent phenomenon of thermal expansion mismatch between materials. However, the expensive raw materials and complex synthesis steps limit its practical application. In this work, we have designed a more advantageous method for the synthesis of NTE material CaZrF6, and it is expected to be generalized to the synthesis of other double ReO3-fluorides. Intriguingly, a new orthorhombic phase CaZrF6 has been synthesized via this method in a lower temperature. Unlike the strong isotropic NTE of the cubic phase CaZrF6, the orthorhombic phase shows the strong anisotropic positive thermal expansion (PTE). The combined analysis of temperature-dependent X-ray diffraction (XRD), Raman spectra, and first-principles calculations shows that the low frequency phonon vibration mode with negative Grüneisen parameter in cubic CaZrF6 are strongly correlated with the transverse thermal vibration of F atoms and dominates the NTE of the material. [ABSTRACT FROM AUTHOR]

This study presents the findings of a vibrational analysis of fayalite (Fe2SiO4) employing normal coordinate analysis rooted in a short-range force model. By employing this methodology, the Raman and IR wave numbers for Fe2SiO4 were thoroughly investigated. The lattice dynamical calculations integrated fifteen stretching and ten bending force constants within the framework of Wilson's GF matrix method. Notably, the outcomes reveal a strong concurrence between the optical vibrational modes computed at the zone center and the existing findings. Furthermore, a comprehensive analysis of mode assignment for the calculated Raman and infrared phonons has been conducted. The study culminates in a theoretical examination of the vibrational phonons, followed by an insightful analysis of potential energy distribution, underscoring the contribution of interatomic forces to the calculated Raman and infrared phonons. [ABSTRACT FROM AUTHOR]

Chromium tri-iodide (CrI3) is a prototypical ferromagnetic van der Waals insulator with its genuinely two-dimensional (2D) long-range magnetic order below 45 K demonstrated recently. The underlying magnetic anisotropy has not been completely understood while both the Dzyaloshinskii-Moriya (DM) interaction and the Kitaev − Γ type interaction have been considered as the relevant magnetic Hamiltonian. In addition, the relation between the crystal structure and the magnetic order needs to be further elucidated concerning their possible coupling in few-layer samples and in the topmost surface layers of bulk samples. Here, we investigate these issues via temperature- and magnetic field-dependent terahertz spectroscopy on bulk CrI3 single crystals, focusing on the dynamics of ferromagnetic resonances (FMRs) and optical phonons in the terahertz (THz) region from 4 to 120 cm−1 (from 0.5 to 15 meV). We narrow down the possible ranges of the interaction parameters such as the off-diagonal symmetric terms and the single-ion anisotropy. The accurate values of these parameters significantly constrain the magnitude of possible Kitaev − Γ exchange interaction and the topological magnon gap. Moreover, the structure-magnetism relationship was critically analyzed based on the temperature- and field-dependences of two E u in-plane optical phonon modes, which shows that the commonly believed structural phase diagram of CrI3, derived from surface-preferential data, has to be seriously modified. [ABSTRACT FROM AUTHOR]

We report a theoretical investigation of the ultrafast dynamics of electrons and phonons in strained monolayer WS2 following photoexcitation. We show that strain substantially modifies the phase space for electron-phonon scattering, unlocking relaxation pathways that are unavailable in the pristine monolayer. In particular, strain triggers a transition between distinct dynamical regimes of the non-equilibrium lattice dynamics characterized by the emission of chiral phonons under high strain and linearly-polarized phonons under low strain. For valley-polarized electronic excitations, this mechanism can be exploited to selectively activate the emission of chiral phonons – phonons carrying a net angular momentum. Our simulations are based on state-of-the-art ab-initio methods and focus exclusively on realistic excitation and strain conditions that have already been achieved in recent experimental studies. Overall, strain emerges as a powerful tool for controlling chiral phonons emission and relaxation pathways in multivalley quantum materials. [ABSTRACT FROM AUTHOR]

Metallic microlattice (MML) materials enable novel material properties through geometry and topology, and through additive manufacturing (AM) there exists a viable and scalable method of producing the fine networks of struts and nodes which make up an architected lattice. However, AM methods often induce locally high cooling rates, which lead to residual strains and anisotropic microstructures which can limit how tunable and predictable the properties of a lattice will be across its volume. Residual strains can degrade mechanical properties or act as strain concentrators and contribute to the failure dynamics of a lattice under load. In the micron scale regime of lattices this means the microstructure is the point of failure minimization, and we show that the orientation of a strut between two edge cases within a lattice and its proximity to a heatsink will change the strain distribution and microstructure within a lattice strut depending on the manufacturing technology used. We show that changes in energy density and solidification conditions between two AM methods, laser and electron beam powder bed fusion (PBF-LB and PBF-EB) lead to different magnitudes of residual strain and anisotropy, with PBF-EB showing far lower levels of residual strain and greater consistency in both strain and microstructure invariant of strut orientation next to a heatsink. [ABSTRACT FROM AUTHOR]

Under investigation in this paper is the inverse scattering transform for a nonlinear lattice equation, which can be used to study the fluctuation of nonlinear optics and dynamics of anharmonic lattices. Symmetries, analyticities and asymptotic behaviors of eigenfunctions will be obtained in the direct scattering analysis to establish a suitable Riemann-Hilbert problem. The Riemann-Hilbert problem of the scattering data with simple poles will be constructed. In particular, by using the Laurent expansion and the generalized residue condition to solve the Riemann-Hilbert problem, the determinant representation of N-soliton solution for the equation will be presented. One-dark-soliton under non-vanishing boundary conditions will be displayed through some representative reflectionless potentials. [ABSTRACT FROM AUTHOR]

Halide perovskites show great optoelectronic performance, but their favorable properties are paired with unusually strong anharmonicity. It was proposed that this combination derives from the ns2 electron configuration of octahedral cations and associated pseudo-Jahn–Teller effect. We show that such cations are not a prerequisite for the strong anharmonicity and low-energy lattice dynamics encountered in these materials. We combine X-ray diffraction, infrared and Raman spectroscopies, and molecular dynamics to contrast the lattice dynamics of CsSrBr3 with those of CsPbBr3, two compounds that are structurally similar but with the former lacking ns2 cations with the propensity to form electron lone pairs. We exploit low-frequency diffusive Raman scattering, nominally symmetry-forbidden in the cubic phase, as a fingerprint of anharmonicity and reveal that low-frequency tilting occurs irrespective of octahedral cation electron configuration. This highlights the role of structure in perovskite lattice dynamics, providing design rules for the emerging class of soft perovskite semiconductors. By comparing CsSrBr3 and CsPbBr3 with close structural similarity but the latter lacking lone-pair electrons on the octahedral metal, the authors reveal the similar vibrational anharmonicities in the two perovskites, which disentangles the electronic properties and vibrational anharmonicities. [ABSTRACT FROM AUTHOR]

Raman spectroscopy together with density functional calculations were used to study lattice dynamics in a layered honeycomb cobaltite Na3Co2SbO6, which can host a field-induced phase related with the Kitaev physics. We show that there develops an additional mode well above Neel temperature (at K) at 525 cm–1, which origin can be related to electronic excitation to one of doublets. Moreover, our theoretical calculations demonstrate that the highest frequency intensive mode related to the oxygen vibrations is very sensitive to type of the magnetic order. Thus, we propose to use the softening of this mode as a hallmark of the transition to a fully polarized regime, which is stabilized in Kitaev materials in strong magnetic fields. [ABSTRACT FROM AUTHOR]

In this article, we focus on a specific version of the NDDEs which is the relativistic Toda lattice equation. We employ the generalized exponential rational function method on a nonlinear model of surface wave propagation to recognize their diverse singular soliton and multi-soliton wave structures. What is remarkable in this article is the use of graphic diagrams, which have diversified the solutions for solving such equations, leading to a greater understanding of the movements of particles and the strengthening of nonlinear lattice dynamics. The efficiency and strength of the employed method are illustrated, signifying its applicability to a wide spectrum of NDDEs in physical phenomena. [ABSTRACT FROM AUTHOR]

Raman spectroscopy together with density functional calculations were used to study lattice dynamics in a layered honeycomb cobaltite Na3Co2SbO6, which can host a field-induced phase related with the Kitaev physics. We show that there develops an additional mode well above Neel temperature (at K) at 525 cm–1, which origin can be related to electronic excitation to one of doublets. Moreover, our theoretical calculations demonstrate that the highest frequency intensive mode related to the oxygen vibrations is very sensitive to type of the magnetic order. Thus, we propose to use the softening of this mode as a hallmark of the transition to a fully polarized regime, which is stabilized in Kitaev materials in strong magnetic fields. [ABSTRACT FROM AUTHOR]

While phonon anharmonicity affects lattice thermal conductivity intrinsically and is difficult to be modified, controllable lattice defects routinely function only by scattering phonons extrinsically. Here, through a comprehensive study of crystal structure and lattice dynamics of Zintl-type Sr(Cu,Ag,Zn)Sb thermoelectric compounds using neutron scattering techniques and theoretical simulations, we show that the role of vacancies in suppressing lattice thermal conductivity could extend beyond defect scattering. The vacancies in Sr2ZnSb2 significantly enhance lattice anharmonicity, causing a giant softening and broadening of the entire phonon spectrum and, together with defect scattering, leading to a ~ 86% decrease in the maximum lattice thermal conductivity compared to SrCuSb. We show that this huge lattice change arises from charge density reconstruction, which undermines both interlayer and intralayer atomic bonding strength in the hierarchical structure. These microscopic insights demonstrate a promise of artificially tailoring phonon anharmonicity through lattice defect engineering to manipulate lattice thermal conductivity in the design of energy conversion materials. [ABSTRACT FROM AUTHOR]

The monolayered tetragonal (Sr, Ba)2ZrO4 compounds, characterized by symmetry and phase I4/mmm (Z = 2), have undergone analysis to determine the Raman and Infrared (IR) phonons using normal coordinates. These compounds, namely Sr2ZrO4 and Ba2ZrO4, represent the initial members of the (Sr, Ba)n+1ZrO3n + 1 Ruddlesden-Popper (RP) series with n = 1. Theoretical calculations have been performed for the optical phonons of the Sr2ZrO4 and Ba2ZrO4 compounds in phase I4/mmm, incorporating nine Short-Range Force Constants (SRFC) for the first time. Assignments of the optical vibrational modes for the (Sr, Ba)2ZrO4 compounds were established by comparing them with available data from isostructural compounds, utilizing Wilson's GF-Matrix Method. The analysis further encompassed investigating the effects of cation-A (A = Sr, Ba) exchange on the lattice dynamics of the monolayered tetragonal A2ZrO4 (A = Sr, Ba) isostructural compounds. This analysis involved a comparison of Zone Centre vibrational modes, force constants, and bond lengths to evaluate the impact of the exchange. Additionally, for each normal mode in the Ruddlesden-Popper phase A2ZrO4 (A = Sr, Ba), the Potential Energy Distribution (PED) was analyzed to elucidate the considerable influence of short-range force constants on the calculated phonons. [ABSTRACT FROM AUTHOR]

The rapid progress of modern technologies has accelerated the prominence of thermal expansion mismatch between materials, and tunable thermal expansion materials will be a powerful safeguard against this challenge. Here, isotropic MHfF6 (M = Ca, Mn, Fe, and Co) compounds with tunable thermal expansion have been produced via a low-cost synthetic method and investigated. By utilizing temperature dependent X-ray diffraction (XRD) and Raman spectroscopy, combined with first principles calculations, it was revealed that the transverse thermal vibrations of the F atoms are dominated by low-frequency phonons with negative Grüneisen parameters and are therefore the origin of the negative thermal expansion (NTE). Very interestingly, with the increase of the M atomic number, the metal⋯F atomic linkages become stiffer, reducing the number of vibrational modes with negative Grüneisen parameters, so that the strong NTE can be gradually adjusted to moderate NTE and to near zero thermal expansion. The present study achieves the tunable thermal expansion in a new compound family and shed light on the internal mechanism from the perspective of lattice vibrational dynamics. [ABSTRACT FROM AUTHOR]

Local constraint in the lattice gauge theory provides an exotic mechanism that facilitates the disorder-free localization. However, the understanding of nonequilibrium dynamics in the non-Hermitian lattice gauge model remains limited. Here, we investigate the quench dynamics in a system of spinless fermions with nonreciprocal hopping in the Z 2 gauge field. By employing a duality mapping, we systematically explore the non-Hermitian skin effect, localization-delocalization transition, and real-complex transition. Through the identification of diverse scaling behaviors of quantum mutual information for fermions and spins, we propose that the non-Hermitian quantum disentangled liquids exist both in the localized and delocalized phases, the former originates from the Z 2 gauge field and the latter arises from the non-Hermitian skin effect. Furthermore, we demonstrate that the nonreciprocal dissipation causes the flow of quantum information. Our results provide valuable insights into the nonequilibrium dynamics in the gauge field, and may be experimentally validated using quantum simulators. Lattice gauge theory, a subset of gauge theory, has been successfully applied to a range of quantum systems allowing for the investigation of localised phenomena within these systems. Here, the authors consider a non-Hermitian lattice model observing a quantum disentangled liquid state that exists in both the localised and delocalised phases. [ABSTRACT FROM AUTHOR]

Understanding the lattice dynamics and heat transport physics in the lead-free halide double perovskites remains an outstanding challenge due to their lattice dynamical instability and strong anharmonicity. In this work, we investigate the microscopic mechanisms of anharmonic lattice dynamics and thermal transport in lead-free halide double perovskite Cs2AgBiBr6 from first principles. We combine self-consistent phonon calculations with bubble diagram correction and a unified theory of lattice thermal transport that considers both the particle-like phonon propagation and wave-like tunnelling of phonons. An ultra-low thermal conductivity at room temperature (~0.21 Wm−1K−1) is predicted with weak temperature dependence(~ T−0.34), in sharp contrast to the conventional ~T−1 dependence. Particularly, the vibrational properties of Cs2AgBiBr6 are featured by strong anharmonicity and wave-like tunnelling of phonons. Anharmonic phonon renormalization from both the cubic and quartic anharmonicities are found essential in precisely predicting the phase transition temperature in Cs2AgBiBr6 while the negative phonon energy shifts induced by cubic anharmonicity has a significant influence on particle-like phonon propagation. Further, the contribution of the wave-like tunnelling to the total thermal conductivity surpasses that of the particle-like propagation above around 310 K, indicating the breakdown of the phonon gas picture conventionally used in the Peierls-Boltzmann Transport Equation. Importantly, further including four-phonon scatterings is required in achieving the dominance of wave-like tunnelling, as compared to the dominant particle-like propagation channel when considering only three-phonon scatterings. Our work highlights the importance of lattice anharmonicity and wave-like tunnelling of phonons in the thermal transport in lead-free halide double perovskites. [ABSTRACT FROM AUTHOR]

The electron excitations dynamics in spherical Au/SiO 2 core-shell nanoparticles excited by 150 fs laser pulses at wavelength of 400 nm was studied by femtosecond transient absorption spectroscopy. It is shown that the electron–phonon and phonon-phonon relaxation times in a nanoparticle increase in the presence of SiO 2 dielectric shell. The obtained transient extinction kinetics of NPs was used to fit the theoretical profile with the relaxation temperature of the excitation dynamics of electron and lattice nanoparticles, as well as their environment under the laser pulses action. The electron–phonon coupling and phonon-phonon relaxation constants for Au/SiO 2 NPs and Au NPs have been established. For Au/SiO 2 core-hell nanoparticles, the electron–phonon coupling constant was γ c o r e / s h e l l = 5 · 10 16 W · m - 3 · K - 1 , and the heat loss constant was h c o r e / s h e l l = 4 · 10 8 W · m - 2 · K - 1 . In the case of gold nanospheres, these constants are γ NPs = 7 · 10 16 W · m - 3 · K - 1 and h NPs = 8 · 10 8 W · m - 2 · K - 1 , respectively. It is concluded that the SiO 2 dielectric shell prevents the defragmentation of the gold core when it reaches the melting point. [ABSTRACT FROM AUTHOR]

The bandgap of inorganic halide perovskites plays a crucial role in the efficiency of solar cells. Although density functional theory can be used to calculate the bandgap of materials, the method is time-consuming and requires deep knowledge of theoretical calculations, theoretical calculations are frequently constrained by complex electronic correlations and lattice dynamics, resulting in discrepancies between calculated and experimental results. To address this issue, this study employs machine learning to predict the bandgap of inorganic halide perovskites. The XGBoost classifier classifies ABX3-type inorganic halide perovskites into narrow and wide bandgap materials. The study collected a dataset consisting of 447 perovskites and generated material descriptors using the Matminer Python package. The model predicts narrow-bandgap materials with 95% accuracy. Finally, the Shapley analysis revealed that the key factor affecting the bandgap of perovskites is the electronegativity range. As the range of electronegativity increases, so does the possibility of a perovskite with a narrow bandgap. These findings highlight the powerful ability of machine learning to quickly and accurately predict the bandgap of perovskites. [ABSTRACT FROM AUTHOR]

The reversible phase transitions in phase-change memory devices can switch on the order of nanoseconds, suggesting a close structural resemblance between the amorphous and crystalline phases. Despite this, the link between crystalline and amorphous tellurides is not fully understood nor quantified. Here we use in-situ high-temperature x-ray absorption spectroscopy (XAS) and theoretical calculations to quantify the amorphous structure of bulk and nanoscale GeTe. Based on XAS experiments, we develop a theoretical model of the amorphous GeTe structure, consisting of a disordered fcc-type Te sublattice and randomly arranged chains of Ge atoms in a tetrahedral coordination. Strikingly, our intuitive and scalable model provides an accurate description of the structural dynamics in phase-change memory materials, observed experimentally. Specifically, we present a detailed crystallization mechanism through the formation of an intermediate, partially stable 'ideal glass' state and demonstrate differences between bulk and nanoscale GeTe leading to size-dependent crystallization temperature. The structure of an ideal glass, crystallisation mechanism, nanoscale effects, and even parallels to organic chemistry can be drawn by conceptualizing the amorphous GeTe structure as a superposition of Te and Ge lattices with atom-specific dynamics. [ABSTRACT FROM AUTHOR]

A chemically homogeneous structure models were established for the multi-principal alloy CoCrFeMnNi and the quaternary CrFeMnNi, CoFeMnNi, CoCrMnNi, CoCrFeNi, and CoCrFeMn alloys, and calculations were performed based on vacancy diffusion mechanism using lattice dynamics and molecular dynamics methods for the self-diffusion of each component atom. By calculating four thermodynamic parameters, namely, vacancy formation energy, atomic migration energy, formation entropy, and effective frequency at the transition state, the self-diffusion properties of each component atom were obtained. The formation energy, migration energy, and formation entropy of each component in different alloys were relatively close. The Arrhenius form of diffusion for each component in the quinary alloy showed that the results modified by experimental values using molecular dynamics were close to the measured values within a given temperature range. Directly substituting the thermodynamic parameters yielded results with some deviation from the measured values, with Mn and Cr exhibiting greater deviations. By substituting experimental values for formation energies, the result for Mn was close to the measured value, while the deviation of Cr data was still relatively large. This might be due to the error in the potential describing the formation energy and effective frequency. Calculating the thermodynamic parameters for quaternary alloys allowed the diffusion Arrhenius form to be obtained. The diffusion coefficient of Mn was much higher than that of other elements, while that of Cr was at a lower level, and the diffusion coefficients of Fe, Co, and Ni were close. In multi-principal alloy systems, there are interactions between the components that affect diffusion behavior, and the degree of influence varies depending on the component type. It seems that Co, Cr, and Mn tend to promote self-diffusion, while Fe and Ni tend to hinder diffusion in these alloys. [ABSTRACT FROM AUTHOR]

The frontiers of material corrosion research are transitioning from macroscopic corrosion to the micro or even nanoscale. The presence of a substantial number of simulated atoms in metal nanomaterials introduces considerable complexity when studying corrosion mechanisms. Therefore, under the framework of lattice dynamics, combined with nano-thermodynamic theory, the electrochemical Butler-Volmer (BV) equation is developed to simplify the investigation of the anodic dissolution behavior of nanomaterials. The results show that the difference between the lattice parameters optimized using the General Utility Lattice Program (GULP) and the Cambridge Sequential Total Energy Package (CASTEP) results is 0.01 Å, and the variation in cohesion and surface energies is only 0.001 eV and 0.005 eV/Å2. Meanwhile, the anodic dissolution rates of Magnesium (Mg) at the (0001), (10一0), and (111一0)2 crystal planes calculated from the BV model based on lattice dynamics are in agreement with the results derived from first principles. During the active dissolution zone, the corrosion potential increases from -6.91 V vs. SHE to -5.02 V vs. SHE, and the corrosion current density (Log i) decreases from 42.27 A/cm2 to 26.47 A/cm2 as the Mg nanoparticles size increases from 1 nm to 7.5 nm. The improved model quantifies the relationship between surface properties and corrosion behavior through the size effect of nanoparticles, which enriches the way of studying electrochemical properties at the nanoscale. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) are an incredibly diverse group of highly porous hybrid materials, which are interesting for a wide range of possible applications. For a meaningful theoretical description of many of their properties accurate and computationally highly efficient methods are in high demand. These would avoid compromises regarding either the quality of modelling results or the level of complexity of the calculated properties. With the advent of machine learning approaches, it is now possible to generate such approaches with relatively little human effort. Here, we build on existing types of machine-learned force fields belonging to the moment-tensor and kernel-based potential families to develop a recipe for their efficient parametrization. This yields exceptionally accurate and computationally highly efficient force fields. The parametrization relies on reference configurations generated during molecular dynamics based, active learning runs. The performance of the potentials is benchmarked for a representative selection of commonly studied MOFs revealing a close to DFT accuracy in predicting forces and structural parameters for a set of validation structures. The same applies to elastic constants and phonon band structures. Additionally, for MOF-5 the thermal conductivity is obtained with full quantitative agreement to single-crystal experiments. All this is possible while maintaining a very high degree of computational efficiency. The exceptional accuracy of the parameterized force field potentials combined with their computational efficiency has the potential of lifting the computational modelling of MOFs to the next level. [ABSTRACT FROM AUTHOR]

Periodic band structures are a hallmark phenomenon of condensed matter physics. While often imposed by external potentials, periodicity can also arise through the interplay of couplings that are not necessarily spatially periodic on their own, but this option is generally less explored than the fully-periodic counterpart. Here, we investigate dynamics in a lattice structure that emerges from the simultaneous application of Raman and radio frequency coupling to a dilute-gas Bose-Einstein condensate. We elaborate on the role of Galilean invariance in this system and demonstrate a variety of techniques, including Bloch oscillations and lattice shaking with spin and momentum resolved measurements. This combined coupling scheme allows for tunability and control, enabling future investigations into unconventional band structures such as quasi-flat ground bands and those with semimetal-like band gaps. The lack of Galilean invariance in spin-orbit coupled systems greatly reduces the controllability of optical lattices and strongly limits applications. By simultaneously applying Raman and radio frequency coupling to a dilute-gas Bose-Einstein condensate, the authors generate an emerging lattice with restored Galilean invariance. [ABSTRACT FROM AUTHOR]

The recent observations of exotic quantum phenomena in AV3Sb5 (A = K, Rb, Cs) kagome superconductors have attracted significant attention in materials physics. Here, we propose an innovative two-frequencies laser model for ultrafast control of transient structural distortions. Using first-principles density functional theory in conjunction with the perturbative regime of nonlinear phononics, we investigate the nonharmonic potential energy, the crystal lattice dynamics and the topological properties of CsV3Sb5. We find that driving two infrared-active phonons of different frequencies promotes the desired Raman phonon vibrations, in which the displacement of Sb atoms is closely related to superconductivity. We demonstrate that the dimensional crossover and the topological nontrivial to trivial state transition of superconductor CsV3Sb5 can be triggered by ultrafast optical control. This work can be applied to other layered quantum materials and provide guidance for experiments related to photoinduced topology and superconductivity. [ABSTRACT FROM AUTHOR]

Currently, there is rapid development of thermophysics of solids associated with the need to create models with a high degree of predictive reliability. This paper presents new approaches to solve relevant issues related to the study of heat transfer in semiconductors and dielectrics, mainly concerning nanostructures. The first of the considered tasks is the creation of a statistical model of the processes of interaction of heat carriers, phonons, with the rough surfaces of solids. For the first time, the authors propose a method based on the statistics of the slopes of the profile of a random surface. The calculation results are the mean free paths of phonon between the opposite boundaries of the sample, which are necessary for calculating the effective thermal conductivity in the ballistic and diffusion–ballistic regime of heat transfer, depending on the roughness parameters. The second task is to develop methods for calculating the processes of heat transfer through the contact surfaces of solids. We are able to show that, taking into account the phonon dispersion and the corresponding restrictions on the frequency values, the modified acoustic mismatch model for calculating Kapitza resistance can be extended to temperatures above 300 K. Previously, the limit of applicability of this method was considered to be a temperature of 30 K. Moreover, the proposed method is also generalized to the case of rough interfaces. The third task is a new approach to determine the thermal conductivity of solids. The authors develop a method of direct Monte Carlo simulation of phonon kinetics with strict consideration of their interaction due to the direct use of the laws of conservation of energy and quasi-momentum. The calculations of the thermal conductivity coefficient for pure silicon in the temperature range from 100 to 300 K show close agreement with the experiment and ab initio calculations of other authors, and also allow considering in details the kinetics of phonons. [ABSTRACT FROM AUTHOR]

The recent observations of exotic quantum phenomena in AV3Sb5 (A = K, Rb, Cs) kagome superconductors have attracted significant attention in materials physics. Here, we propose an innovative two-frequencies laser model for ultrafast control of transient structural distortions. Using first-principles density functional theory in conjunction with the perturbative regime of nonlinear phononics, we investigate the nonharmonic potential energy, the crystal lattice dynamics and the topological properties of CsV3Sb5. We find that driving two infrared-active phonons of different frequencies promotes the desired Raman phonon vibrations, in which the displacement of Sb atoms is closely related to superconductivity. We demonstrate that the dimensional crossover and the topological nontrivial to trivial state transition of superconductor CsV3Sb5 can be triggered by ultrafast optical control. This work can be applied to other layered quantum materials and provide guidance for experiments related to photoinduced topology and superconductivity. [ABSTRACT FROM AUTHOR]

A novel inorganic polymers and organic spacers (IPOS) derivative strontium cobalt chloride bis 15-crown-5-ether tetra ammonium thiocyanate (SCCTC) single crystal synthesis via solution growth technique. Initially, the detailed crystallography information of cell parameters and data structure were carried out by single crystal X-ray diffraction studies, which reveal that the orthorhombic system acquires centrosymmetric space group of Pnma. As-grown crystal chemical bonding assignments, elemental compositions confirmed by using energy dispersive X-ray and vibrational spectroscopy. Additionally, H-bond present in the prepared sample identified by CHNS analysis. In this work, the cut-off wavelength was found at 353 nm with band gap (Tauc's plot) of 3.22 eV can be ascertained from the UV–Visible-NIR spectrum. The prominent crystal growth mechanism were examined by using scanning electron microscope, chemical etching study to correlate the surface texture and reverse growth rate etch pattern. For device fabrication, lattice dynamics, thermal and mechanical properties are necessary for testing the sample assessment by thermogravimetric, Vickers hardness and dielectric measurement. Using single beam Z-scan technique under 633 nm excitation were carried out experimentally non-linear susceptibility, absorption coefficient and refractive index. The above results suggest that grown crystals have good transmittance, moderate thermal, mechanical and large susceptibility values. So, these properties turn into be potential materials for making optical device applications. [ABSTRACT FROM AUTHOR]

Controlling the selectivity of the electrocatalytic reduction of carbon dioxide into value-added chemicals continues to be a major challenge. Bulk and surface lattice strain in nanostructured electrocatalysts affect catalytic activity and selectivity. Here, we unravel the complex dynamics of synergistic lattice strain and stability effects of Cu-Ag tandem catalysts through a previously unexplored combination of in situ nanofocused X-ray absorption spectroscopy and Bragg coherent diffraction imaging. Three-dimensional strain maps reveal the lattice dynamics inside individual nanoparticles as a function of applied potential and product yields. Dynamic relations between strain, redox state, catalytic activity and selectivity are derived. Moderate Ag contents effectively reduce the competing evolution of H2 and, concomitantly, lead to an enhanced corrosion stability. Findings from this study evidence the power of advanced nanofocused spectroscopy techniques to provide new insights into the chemistry and structure of nanostructured catalysts. Combining in situ nanoprobe techniques paves the way for gaining insights into structure-selectivity relations for electrocatalysts. Herein, the dynamic evolution of lattice strain in individual nanoparticles is directly visualized with nanoscale resolution in Cu-Ag tandem catalysts during the electrocatalytic conversion of CO2 into value-added chemicals. [ABSTRACT FROM AUTHOR]

The structures, strain fields, and defect distributions in solid materials underlie the mechanical and physical properties across numerous applications. Many modern microstructural microscopy tools characterize crystal grains, domains and defects required to map lattice distortions or deformation, but are limited to studies of the (near) surface. Generally speaking, such tools cannot probe the structural dynamics in a way that is representative of bulk behavior. Synchrotron X-ray diffraction based imaging has long mapped the deeply embedded structural elements, and with enhanced resolution, dark field X-ray microscopy (DFXM) can now map those features with the requisite nm-resolution. However, these techniques still suffer from the required integration times due to limitations from the source and optics. This work extends DFXM to X-ray free electron lasers, showing how the 10 12 photons per pulse available at these sources offer structural characterization down to 100 fs resolution (orders of magnitude faster than current synchrotron images). We introduce the XFEL DFXM setup with simultaneous bright field microscopy to probe density changes within the same volume. This work presents a comprehensive guide to the multi-modal ultrafast high-resolution X-ray microscope that we constructed and tested at two XFELs, and shows initial data demonstrating two timing strategies to study associated reversible or irreversible lattice dynamics. [ABSTRACT FROM AUTHOR]

Research on charge-density-wave (CDW) ordered transition-metal dichalcogenides continues to unravel new states of quantum matter correlated to the intertwined lattice and electronic degrees of freedom. Here, we report an inelastic x-ray scattering investigation of the lattice dynamics of the canonical CDW compound 2H-TaSe2 complemented by angle-resolved photoemission spectroscopy and density functional perturbation theory. Our results rule out the formation of a central-peak without full phonon softening for the CDW transition in 2H-TaSe2 and provide evidence for a novel precursor region above the CDW transition temperature TCDW, which is characterized by an overdamped phonon mode and not detectable in our photoemission experiments. Thus, 2H-TaSe2 exhibits structural before electronic static order and emphasizes the important lattice contribution to CDW transitions. Our ab-initio calculations explain the interplay of electron-phonon coupling and Fermi surface topology triggering the CDW phase transition and predict that the CDW soft phonon mode promotes emergent superconductivity near the pressure-driven CDW quantum critical point. The authors study the charge-density-wave (CDW) compound 2H-TaSe2 by inelastic x-ray scattering combined with photoemission spectroscopy. They find evidence for a precursor region above the CDW transition temperature, which is characterized by an overdamped phonon mode and is not detectable by photoemission. [ABSTRACT FROM AUTHOR]

Efficient generation and control of spin currents launched by terahertz (THz) radiation with subsequent ultrafast spin-to-charge conversion is the current challenge for the next generation of high-speed communication and data processing units. Here, we demonstrate that THz light can efficiently drive coherent angular momentum transfer in nanometer-thick ferromagnet/heavy-metal heterostructures. This process is non-resonant and does neither require external magnetic fields nor cryogenics. The efficiency of this process is more than one order of magnitude higher as compared to the recently observed THz-induced spin pumping in MnF2 antiferromagnet. The coherently driven spin currents originate from the ultrafast spin Seebeck effect, caused by a THz-induced temperature imbalance in electronic and magnonic temperatures and fast relaxation of the electron-phonon system. Owing to the fact that the electron-phonon relaxation time is comparable with the period of a THz wave, the induced spin current results in THz second harmonic generation and THz optical rectification, providing a spintronic basis for THz frequency mixing and rectifying components. Terahertz frequencies offer the potential of much higher data transfer rates, but this requires devices able to generate and manipulate terahertz waves. One approach is to utilize the spin dynamics of a magnetic system. Here, Ilyakov et al. show how a multilayer magnetic and heavy-metal heterostructure can be used to achieve terahertz second harmonic generation and optical rectification. [ABSTRACT FROM AUTHOR]

Micro-Raman spectroscopy and X-ray diffraction have been used to explore the lattice dynamics of Nb-substituted SrBi2(Ta1-xNbx)2O9 (SBTN) crystalline thin films annealed at low temperature, 700 °C. It turned out that SrBi2(Ta1-xNbx)2O9 films consist of fine-grained spherical structures for x = 0.1–0.4, while the formation of rod-like grains occurs for x = 0.5 due to the stress-induced transformation of the thin film perovskite structure. Moreover, it was revealed that during Nb cationic substitution Aurivillius phase formation was enhanced and became dominated in SBTN thin films and fluorite/pyrochlore phase formation was highly suppressed. We assume that these changes are conditioned by the ferrodistortion occurring in ferroic perovskites, namely by the tilting distortion of (Ta,Nb)O6 octahedra for x = 0.2–0.5. The octahedral tilting distortion can change the coordination environment of the A-cite cation, as well as it lowers the SBTN symmetry due to the differences in ionic radius and mass between Ta and Nb in the B-sites that can lead to significant changes of the SBTN crystal structure. The same nonmonotonic trends were observed for the ferroelectric perovskite phase fraction and remanent polarization on Nb content in SBTN films. The substituting Nb atoms with a concentration of 10–20% made it possible to increase the remanent polarization in 3 times and raise the perovskite phase fraction from 66 to 87%. Therefore, obtained results can be used for the production of lead-free thin films with a high remanent polarization under low annealing temperature, being promising for advanced nonvolatile random access ferroelectric memory (NvFeRAM) applications. [ABSTRACT FROM AUTHOR]

The quantum nature of the hydrogen lattice in superconducting hydrides can have crucial effects on the material's properties. Taking a detailed look at the dynamic stability of the recently predicted BaSiH8 phase, we find that the inclusion of anharmonic quantum ionic effects leads to an increase in the critical dynamical pressure to 20 GPa as compared to 5 GPa within the harmonic approximation. We identify the change in the crystal structure due to quantum ionic effects to be the main driving force for this increase and demonstrate that this can already be understood at the harmonic level by considering zero-point energy corrections to the total electronic energy. In fact, the previously determined critical pressure of kinetic stability pkin = 30 GPa still poses a stricter bound for the synthesizability of BaSiH8 and similar hydride materials than the dynamical stability and therefore constitutes a more rigorous and accurate estimate for the experimental realizability of these structures. The quantum nature of the hydrogen lattice in superconducting hydrides can have crucial effects on the material's properties. In this work, the authors focus on the low-pressure superconductor BaSiH8 and identify the structural change due to quantum ionic effects to be the main driving force in increasing the critical pressure of dynamic stability. [ABSTRACT FROM AUTHOR]

Kagomé metals are widely recognized, versatile platforms for exploring topological properties, unconventional electronic correlations, magnetic frustration, and superconductivity. In the RV6Sn6 family of materials (R = Sc, Y, Lu), ScV6Sn6 hosts an unusual charge density wave ground state as well as structural similarities with the AV3Sb5 system (A = K, Cs, Rb). In this work, we combine Raman scattering spectroscopy with first-principles lattice dynamics calculations to reveal phonon mixing processes in the charge density wave state of ScV6Sn6. In the low temperature phase, we find at least four new peaks in the vicinity of the V-containing totally symmetric mode near 240 cm−1 suggesting that the density wave acts to mix modes of P6/mmm and R 3 ¯ m symmetry - a result that we quantify by projecting phonons of the high symmetry state onto those of the lower symmetry structure. We also test the stability of the short-range ordered density wave state under compression and propose that both physical and chemical pressure quench the effect. We discuss these findings in terms of symmetry and the structure-property trends that can be unraveled in this system. [ABSTRACT FROM AUTHOR]

HIV-1 capsid (CA) stability is important for viral replication. E45A and P38A mutations enhance and reduce core stability, thus impairing infectivity. Second-site mutations R132T and T216I rescue infectivity. Capsid lattice stability was studied by solving seven crystal structures (in native background), including P38A, P38A/T216I, E45A, E45A/R132T CA, using molecular dynamics simulations of lattices, cryo-electron microscopy of assemblies, time-resolved imaging of uncoating, biophysical and biochemical characterization of assembly and stability. We report pronounced and subtle, short- and long-range rearrangements: (1) A38 destabilized hexamers by loosening interactions between flanking CA protomers in P38A but not P38A/T216I structures. (2) Two E45A structures showed unexpected stabilizing CANTD-CANTD inter-hexamer interactions, variable R18-ring pore sizes, and flipped N-terminal β-hairpin. (3) Altered conformations of E45Aa α9-helices compared to WT, E45A/R132T, WTPF74, WTNup153, and WTCPSF6 decreased PF74, CPSF6, and Nup153 binding, and was reversed in E45A/R132T. (4) An environmentally sensitive electrostatic repulsion between E45 and D51 affected lattice stability, flexibility, ion and water permeabilities, electrostatics, and recognition of host factors. The effects of E45A or P38A capsid mutations on HIV core stability and infectivity are reversed by R132T or T216I. Here, authors used structural and biophysical methods to reveal short- and long-range rearrangements that explain stability changes. [ABSTRACT FROM AUTHOR]

Co 2 FeSi Heusler alloys have attracted a lot of attention due to their interesting properties for various technological applications. In this study, we present the results of ab-initio calculations of the electronic, structural and magnetic properties using generalized gradient approximations (GGA and GGA + U). The energies obtained from GGA are used to calculate the magnetic coupling and establish an effective Hamiltonian. Additionally, we utilized mean-field theory and Monte Carlo simulation to evaluate physical properties such as magnetization, susceptibility and critical exponent of the material from the effective Hamiltonian. The results indicate that Co2FeSi, which exhibits a half-metallic behaviour, may be suitable for use in spintronic applications. [ABSTRACT FROM AUTHOR]

The basis for our understanding of quantum magnetism has been the study of elegantly simple model systems. However, even for the antiferromagnetic honeycomb lattice with isotropic spin interactions–one of the simplest model systems–a detailed understanding of quantum effects is still lacking. Here, using inelastic neutron scattering measurements of the honeycomb lattice material YbCl3, we elucidate how quantum effects renormalize the single-magnon and multimagnon excitations and how this renormalization can be tuned and ultimately driven to the classical limit by applying a magnetic field. Additionally, our work reveals that the quantum effects tuned by the magnetic field not only renormalize the magnetic excitations but also induce a distinctive sharp feature inside the multimagnon continuum. From a more general perspective, this result demonstrates that structures within magnetic continua can occur over a wide experimental parameter space and can be used as a reliable means of identifying quantum phenomena. The honeycomb lattice is of fundamental importance for understanding quantum spin liquids and frustrated magnetism more generally. Here, the authors use inelastic neutron scattering to investigate the honeycomb antiferromagnet YbCl3 showing how quantum effects renormalize the single-magnon and multimagnon excitations, shedding further light on the mechanisms of quantum magnetism in honeycomb-lattice compounds. [ABSTRACT FROM AUTHOR]

The basis for our understanding of quantum magnetism has been the study of elegantly simple model systems. However, even for the antiferromagnetic honeycomb lattice with isotropic spin interactions–one of the simplest model systems–a detailed understanding of quantum effects is still lacking. Here, using inelastic neutron scattering measurements of the honeycomb lattice material YbCl3, we elucidate how quantum effects renormalize the single-magnon and multimagnon excitations and how this renormalization can be tuned and ultimately driven to the classical limit by applying a magnetic field. Additionally, our work reveals that the quantum effects tuned by the magnetic field not only renormalize the magnetic excitations but also induce a distinctive sharp feature inside the multimagnon continuum. From a more general perspective, this result demonstrates that structures within magnetic continua can occur over a wide experimental parameter space and can be used as a reliable means of identifying quantum phenomena. The honeycomb lattice is of fundamental importance for understanding quantum spin liquids and frustrated magnetism more generally. Here, the authors use inelastic neutron scattering to investigate the honeycomb antiferromagnet YbCl3 showing how quantum effects renormalize the single-magnon and multimagnon excitations, shedding further light on the mechanisms of quantum magnetism in honeycomb-lattice compounds. [ABSTRACT FROM AUTHOR]

Group I niobates (KNbO3 and NaNbO3) are promising lead-free alternatives for high-performance energy storage applications. Despite their potential, their complex phase transitions arising from temperature-dependent phonon softening and anharmonic effects on dielectric properties remain poorly explored. In this study, we employ density-functional theory (DFT) and self-consistent phonon (SCP) calculations to investigate finite-temperature phonons in cubic niobate perovskites. To include explicit anharmonic vibrational effects, SCP frequencies are shifted by the bubble self-energy correction within the quasiparticle (QP) approximation, providing precise descriptions of phonon softening in these strongly anharmonic solids. We further calculate the static dielectric constant of KNbO3 and NaNbO3 as a function of temperature using the Lyddane-Sachs-Teller (LST) relation and QP-corrected phonon dispersions. Our theoretical results align with experimental data, offering reliable temperature-dependent phonon dispersions while considering anharmonic self-energies and thermal expansion effects, enhancing our understanding of the complex relations between lattice vibrations and phase transitions in these anharmonic oxides. [ABSTRACT FROM AUTHOR]

GaAsBi nanowires represent a novel and promising material platform for future nano-photonics. However, the growth of high-quality GaAsBi nanowires and GaAsBi alloy is still a challenge due to a large miscibility gap between GaAs and GaBi. In this work we investigate effects of Bi incorporation on lattice dynamics and carrier recombination processes in GaAs/GaAsBi core/shell nanowires grown by molecular-beam epitaxy. By employing photoluminescence (PL), PL excitation, and Raman scattering spectroscopies complemented by scanning electron microscopy, we show that increasing Bi-beam equivalent pressure (BEP) during the growth does not necessarily result in a higher alloy composition but largely affects the carrier localization in GaAsBi. Specifically, it is found that under high BEP, bismuth tends either to be expelled from a nanowire shell towards its surface or to form larger clusters within the GaAsBi shell. Due to these two processes the bandgap of the Bi-containing shell remains practically independent of the Bi BEP, while the emission spectra of the NWs experience a significant red shift under increased Bi supply as a result of the localization effect. [ABSTRACT FROM AUTHOR]

We investigate theoretically the lattice motion-induced DC spin current in a coupled spin-lattice system. The XY spin-Peierls model is adopted to mimic the spin lattice interaction, and then via the Jordan–Wigner transformation the S = 1 2 spin system is mapped to a fermion one. By using the quadratic response theory, we demonstrate that a DC spin current can be generated by the lattice wave. The dependence of the spin current on the external magnetic field and the properties of the lattice wave has been addressed. Moreover, it is found that the spin current is linearly proportional to the relaxation time, similar to the injection current in electronic systems. The results suggest the potential of lattice dynamics to produce spin currents in magnetic systems. [ABSTRACT FROM AUTHOR]

Recent experimental studies of the isoscalar giant monopole resonance (ISGMR) region in the Ca isotope chain are analyzed within the microscopic model of the phonon–phonon coupling based on the Skyrme energy-density functional. The inclusion of two- and three-phonon configurations leads to a substantial redistribution of the ISGMR strength to lower energy states and also higher energy tail. It is shown that the gross structure of the ISGMR in the calcium isotopes Ca is caused by the complex configurations. [ABSTRACT FROM AUTHOR]

The nexus between classic ferroelectricity and the structure of perovskite materials hinges on the concept of lattice disorder. Although the ordered perovskites display short-range displacements of the central cations around their equilibrium points, the lattice disorder dynamically unfolds to generate a myriad of distorted rhombohedral lattices characterized by the hopping of the central cations across <111> directions. It is discovered that the lattice disorder correlates with the emergence of minimum configuration energy <100> pathways for the central cations, resulting in spatially modulated ultrafast polarization nanocluster arrangements that are stabilized by the electric charge defects in the material. Through high-resolution phonon dispersion analyses encompassing molecular dynamics (MD) and density functional theory (DFT) simulations, we provide unequivocal evidence linking the hopping of central cations to the development of diffuse soft phonon modes observed throughout the phase transitions of the perovskite. Through massive MD simulations, we unveil the impact of lattice disorder on the structures of domain walls at finite-temperature vis-à-vis collective activation and deactivation of <100> pathways. Furthermore, our simulations demonstrate the development of hierarchical morphotropic phase boundary (MPB) nanostructures under the combined influence of externally applied pressure and stress relaxation, characterized by sudden emergence of zig-zagged monoclinic arrangements that involve dual <111> shifts of the central cations. These findings have implications for tailoring MPBs in thin-film structures and for the light-induced mobilization of DWs. Avenues are finally uncovered to the exploration of lattice disorder through gradual shear strain application. [ABSTRACT FROM AUTHOR]

Various concentrations of europium-doped gadolinium oxide powders are synthesized by a high-temperature solid-state reaction method. Raman spectra of the compounds exhibited the vibrations and symmetry of monoclinic single-phase crystal formation, with the predominant monoclinic phase of Gd2O3 which is consistent with the XRD findings reported earlier. The core level electron emission spectra revealed the formation of highly valence-stable compound systems with shell structures corresponding to Eu3+ and Gd3+ electronic states. In-depth analysis of photoluminescence spectra with multiple emissions in the yellow–red region corresponding to transitions of 5D0–7F2, 5D0–7F1, and 5D0–7F0 which arise due to europium substitution brought out interesting findings of colourinescence parameters. Investigations of Judd–Ofelt parameters, mean lifetimes, radiative transition rates, and CIE coordinates revealed the compatibility of the prepared samples as the good orange-red emitter. [ABSTRACT FROM AUTHOR]

We study the risk management problem of a hydropower producer that hedges risk by trading currency and power futures contracts. The model considers three types of risks: operational risk due to supply uncertainty, profit risk due to power price variability, and exchange rate risk when operation and trading take place in different currencies. We cast the problem as a Markov decision process and propose a sequential solution approach that separates operational management from trading. To solve the problem, we first reduce the high-dimensional Markovian process that models inflows, exchange rates, and future curve dynamics to a scenario lattice and then employ stochastic dual dynamic programming under a risk measure. We find that dynamic hedging leads to significant risk reduction and that it performs better than static hedge ratios that are often used in practice. We also find that a sequential approach leads to better outcomes than an integrated approach across various metrics, which supports the functional separation of operation and hedging that is common practice in most power companies. [ABSTRACT FROM AUTHOR]

We investigate the wavepacket dynamics of quasiparticles in a Su–Schrieffer–Heeger lattice with third-nearest-neighbor hopping. The results reveal that the life-span of Zitterbewegung can be prolonged. To better understand the mechanism, we discuss the band structure and the long-time average of inverse participation rate. The results show that the band structure can be effectively manipulated as a quasi-flat band by introducing the third-nearest-neighbor hopping. This, as a unique advantage over the standard Su–Schrieffer–Heeger model, will bring about restrained diffusion of the wavepacket as well as dramatically stretched life-span of Zitterbewegung, thus will promise wide applications in condensed matter physics. [ABSTRACT FROM AUTHOR]

In this paper, we investigate a discrete relativistic Toda lattice ( dRTL + (α) ) system, which may describe particle vibrations in lattices with an exponential interaction force. First, we construct its discrete generalized (m , 2 N − m) -fold Darboux transformation, from which we can explicitly give its analytic solutions, such as discrete multi-soliton solutions, position controllable rational and semi-rational solutions and their hyperbolic-and-rational mixed solutions, whose properties and dynamics are analyzed and shown graphically. Second, the asymptotic behaviors of diverse exact solutions are analyzed, which shows that the interactions among different solutions are always elastic. In particular, the position of controllable rational solutions and asymptotic state analysis of discrete hyperbolic-and-rational mixed solutions are obtained and discussed for the first time. Finally, we study some integrable properties of this system, such as the integrable hierarchy and relevant Hamiltonian structures and conservation laws from a discrete spectral problem. These results may be helpful for understanding nonlinear lattice dynamics. [ABSTRACT FROM AUTHOR]

Detecting low dose rates of X-rays is critical for making safer radiology instruments, but is limited by the absorber materials available. Here, we develop bismuth oxyiodide (BiOI) single crystals into effective X-ray detectors. BiOI features complex lattice dynamics, owing to the ionic character of the lattice and weak van der Waals interactions between layers. Through use of ultrafast spectroscopy, first-principles computations and detailed optical and structural characterisation, we show that photoexcited charge-carriers in BiOI couple to intralayer breathing phonon modes, forming large polarons, thus enabling longer drift lengths for the photoexcited carriers than would be expected if self-trapping occurred. This, combined with the low and stable dark currents and high linear X-ray attenuation coefficients, leads to strong detector performance. High sensitivities reaching 1.1 × 103 μC Gyair−1 cm−2 are achieved, and the lowest dose rate directly measured by the detectors was 22 nGyair s−1. The photophysical principles discussed herein offer new design avenues for novel materials with heavy elements and low-dimensional electronic structures for (opto)electronic applications. The complex coupling between charge-carriers and phonons in bismuth oxyiodide (BiOI) are uncovered, showing how carrier localisation is avoided and long transport lengths achieved. As a result, BiOI is revealed to be highly effective for X-ray detection. [ABSTRACT FROM AUTHOR]

An isotopic effect arising from the substitution of superheavy water molecules for normal water molecules in ice (Ih) has been studied by the lattice dynamics method in a quasi-harmonic approximation using a rigid three-point potential modified to reproduce the superheavy water properties. It has been shown that the considerable variation of the vibrational state density upon substituting 12.5, 50, and 100% of water molecules takes place only in the range of libration. The temperature dependence of the superheavy ice density has been calculated, and the density maximum for this ice near 60 K has been predicted. A relationship between the melting point of (T2O + H2O)-ice Ih and the T2O molecule concentration in its structure has been constructed, and this relationship has been found to be linear. [ABSTRACT FROM AUTHOR]

Double ReO3-type fluorides have a great interest in the field of negative thermal expansion (NTE) and luminescent materials. However, their application is limited by the scarcity of quantity, expensive raw materials, and harsh preparation conditions. In this work we have found a new NTE material, CaSnF6, by applying the concept of the average atomic volume. More importantly, different from the previous solid-phase sintering and direct fluorination methods, the nano CaSnF6 has been synthesized for the first time by solvothermal method. The results of X-ray diffraction (XRD) and Raman spectroscopy show that a phase transition occurs from rhombohedral (R 3 ¯ ) to cubic (F m 3 ¯ m ) structure at about 200 K, and a strong isotropic NTE (αv = −15.78 × 10−6 K−1) appears in the cubic phase. Lattice dynamics calculations from first-principles illustrate that the NTE is due to the transverse vibration of fluorine atoms excited by low-frequency phonons. This work not only broadens the NTE family of fluorides, but also provides a new facile and low-cost fabricati on method for the preparation of NTE fluorides. [ABSTRACT FROM AUTHOR]

Improving the performance of molecular qubits is a fundamental milestone towards unleashing the power of molecular magnetism in the second quantum revolution. Taming spin relaxation and decoherence due to vibrations is crucial to reach this milestone, but this is hindered by our lack of understanding on the nature of vibrations and their coupling to spins. Here we propose a synergistic approach to study a prototypical molecular qubit. It combines inelastic X-ray scattering to measure phonon dispersions along the main symmetry directions of the crystal and spin dynamics simulations based on DFT. We show that the canonical Debye picture of lattice dynamics breaks down and that intra-molecular vibrations with very-low energies of 1-2 meV are largely responsible for spin relaxation up to ambient temperature. We identify the origin of these modes, thus providing a rationale for improving spin coherence. The power and flexibility of our approach open new avenues for the investigation of magnetic molecules with the potential of removing roadblocks toward their use in quantum devices. Understanding phonon-induced relaxation in molecular qubits is a crucial step in realizing their application potential. Garlatti at al. use a combination of inelastic X-ray scattering and density functional theory to investigate the role of low-energy phonons on spin relaxation of a prototypical molecular qubit. [ABSTRACT FROM AUTHOR]