Quasi-one-dimensional (Q1D) materials featuring chainlike structures with half-filled transition metal $d$ shells offer a unique playground to study emergent spin order and quasiparticle interactions. In this paper, we successfully grow and comprehensively analyze a manganese-based compound, $\mathrm{L}{\mathrm{a}}_3\mathrm{MnB}{\mathrm{i}}_5$, characterized by face-sharing $\mathrm{MnB}{\mathrm{i}}_6$ spin chains. At low temperatures, $\mathrm{L}{\mathrm{a}}_3\mathrm{MnB}{\mathrm{i}}_5$ adopts an antiferromagnetic spin configuration and exhibits various anomalies in both magnetization and specific heat measurements, signatures for successive magnetic phase transitions upon varying temperature. The electrical transport reveals its metallic behavior, likely contributed by the itinerant La electrons. We reveal complex hysteretic behaviors in its magnetoresistance under different transport configurations, indicating the interplay between the interchain and intrachain coupling in this Q1D material. In this paper, we offer insights into the understanding of the unique magnetic and electronic properties of the $R_{3}M{X}_5$ family, and we hope to spark further investigation into the precise magnetic structure and spin physics in similar systems.

${\mathrm{V}}_2{\mathrm{O}}_3$, as a typical strongly correlated material, possesses great application value due to its unique metal-insulator transition property. However, the difficulty of epitaxially growing high-quality ${\mathrm{V}}_2{\mathrm{O}}_3$ thin films on semiconductor substrates has dramatically limited its development in electronic devices. Here, we utilize the similarity of the local structure of the (001) plane to achieve the epitaxial growth of high-quality ${\mathrm{V}}_2{\mathrm{O}}_3$ thin films on the 4H-SiC substrate. By changing the strain in the films to induce the paramagnetic metal (PM) to paramagnetic insulator (PI) transition occurrence, we realize a giant resistivity change ($\mathrm{\Delta }\mathrm{R}/\mathrm{R}=107500\%$) at room temperature. Raman spectra results show that the electrical properties of the strain-controlled films are realized by increasing/decreasing the $a_{1g}$ orbital occupation, supporting the scenario of trigonal distortion, in which the PM-PI transition can be understood as orbital-selective MIT caused by small changes in the trigonal distortion. The ability to epitaxially grow on semiconductor substrates and to modulate electrical properties by strain makes ${\mathrm{V}}_2{\mathrm{O}}_3/\text{4H-SiC}$ thin films an ideal platform for exploring and studying Mott devices.

Machine-learning potentials (MLPs) are advantageous in modeling boron coordination and three-membered rings (3-rings) in borate glasses. In this study, the prominent ability of MLP enables us to study how boron coordination varies during deformation, and the change in microstructure circumvents the overload stress in lithium borate and lithium borosilicate glasses via molecular dynamics simulations. Under uniaxial and triaxial compressive deformations, some of the threefold coordinated boron, ${}^3\mathrm{B}$, atoms were altered to be fourfold coordinated boron (${}^4\mathrm{B}$) at a strain range beyond elastic deformations. According to the local deformation analysis, a microstructure at around ${}^4\mathrm{B}$ was determined to be rigid, specifically, that around ${}^4\mathrm{B}$ forming a 3-ring exhibited the least flexibility. Conversely, the local region at around ${}^3\mathrm{B}$ and oxygen atoms in nonring structures flexibly deformed following the entire deformation. As a result, nonbridging oxygen located in the vicinity of ${}^3\mathrm{B}$ was found to migrate to form ${}^4\mathrm{B}$ due to compression. Remarkably, most of the boron atoms became ${}^4\mathrm{B}$, and they formed abundant three membered rings in the borate glasses at a certain strain owing to the triaxial compression. Consequently, it is inferred that such a drastic structural variation can be the origin of high damage resistance of borate glasses.

ZrGeSe is one of the most well-known topological nodal-line semimetals, which possesses linearly dispersive electronic bands near the Fermi surface. However, the lattice-dynamics study and its interaction with the electronic system have not been investigated. We employed the inelastic neutron-scattering method to study the lattice dynamics of ZrGeSe single crystals. The measured acoustic phonon dispersions were compared with lattice-dynamics calculations, with an overall good agreement with theory; however, both the longitudinal and the transverse acoustic phonon dispersions along the ($q00$) directions demonstrate significant softening, unexpectedly in contrast with the theoretical predictions. Complementary ab initio molecular dynamics simulations indicate an anomalous temperature dependency in the vibrational spectroscopy. We show that strong electron-phonon coupling exists along the Γ-$M-X$ directions and argue that the phonon softening is induced by such electron-phonon coupling.

Low thermal conductivity is important for thermal barrier coatings, thermoelectrics, and other applications in industry and materials science. Accurate calculation of their thermal conductivity $\kappa$ at high temperatures remains challenging: methods such as the Boltzmann transport equation (BTE) usually underestimate the actual value. Here we used the effective harmonic method and homogeneous nonequilibrium molecular dynamics simulations with machine-learning potentials to calculate the thermal conductivity of candidate materials at temperatures up to 1500 K. The results obtained for ${\mathrm{La}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7, {\mathrm{ZrSiO}}_4$, and ${\mathrm{BaZrO}}_3$ are in perfect agreement with the experiment at all temperatures. We used renormalized second- and third-order interatomic force constants and phonons at high temperatures to calculate the thermal conductivity using the BTE and confirmed these results with molecular dynamics simulations. Investigating the relationship of thermal conductivity with the elastic properties, Debye temperature, and the speed of sound, we proposed threshold values for future high-throughput screening for low-$\kappa$ materials. Using the molecular dynamics method at high temperatures, we calculated the volumetric thermal expansion coefficient and selected ten candidate materials for thermal barrier coatings at high temperatures. Besides thermal barrier coating materials, this approach can be applied to multiple classes of materials where thermal conductivity is important.

The paper deals with the U-based compound ${\mathrm{UPt}}_2{\mathrm{Si}}_2$ (UPS). The material was first treated as a localized $5f$ electron system. Later, an opposite opinion of a predominantly itinerant nature of the system was put forward. The most recent publications treat UPS as a dual material. We suggest a material-specific theoretical model based on the density functional theory plus Hubbard $U$ $(\mathrm{DFT}+U)$ calculations that describes the set of fundamental ground-state properties and high magnetic field experiment. The ground-state properties include antiferromagnetic magnetic structure, magnetic easy axis, and the value of the U atomic moment. The in-field experiment shows the presence of a strong metamagnetic transition for the field parallel to the easy axis in contrast to the hard field direction where such a feature is absent. On the other hand, comparable induced magnetization values are obtained for both easy and hard field directions. Within the framework of the suggested model we show that the compound possesses well-formed atomic moments built by electrons treated as delocalized. To understand the experimental high-field properties we estimate exchange energy, magnetic anisotropy energy, and Zeeman energy. All three energies are shown to have comparable values what is crucial for the interpretation of the experiment. At all steps of the study we devote special attention to revealing and emphasizing the dual itinerant-localized properties of the material. The obtained forms of the duality are different: well-defined atomic moments formed by the itinerant electrons, interplay of the single-site and two-site anisotropies, strong localization of two of the $5f$ electrons in contrast to the itinerant nature of the $5f$ electrons contributing to the states around the Fermi level, intense Stoner continuum competing with spin wave formation. The obtained high sensitivity of the calculated properties to the details of the theoretical model reflects the complexity of the multi-orbital $5f$ electron system. The latter is the origin of the wide range of complex behavior observed in U-based materials.

The ability to observe astronomical events through the detection of gravitational waves relies on the quality of multilayer coatings used on the optical mirrors of interferometers. Amorphous ${\mathrm{Ta}}_2{\mathrm{O}}_5$ (including ${\mathrm{TiO}}_2:{\mathrm{Ta}}_2{\mathrm{O}}_5$) currently limits detector sensitivity due to high mechanical loss. In this paper, mechanical loss measured at both cryogenic and room temperatures of amorphous ${\mathrm{Ta}}_2{\mathrm{O}}_5$ films grown by magnetron sputtering and annealed in air at 500 ${}^{\circ }\mathrm{C}$ is shown to decrease for elevated growth temperature. Films grown at 310 ${}^{\circ }\mathrm{C}$ and annealed yield a mechanical loss of $3.1\times {10}^{-4}$ at room temperature, the lowest value reported for pure amorphous ${\mathrm{Ta}}_2{\mathrm{O}}_5$ grown by magnetron sputtering to date, and comparable to the lowest values obtained for films grown by ion beam sputtering. Additionally, the refractive index $n$ increases 6% for elevated growth temperature, which could lead to improved sensitivity of gravitational-wave detectors by allowing a thickness reduction in the mirrors' coatings. Structural characterization suggests that the observed mechanical loss reduction in amorphous ${\mathrm{Ta}}_2{\mathrm{O}}_5$ films with increasing growth temperature correlates with a reduction in the coordination number between oxygen and tantalum atoms, consistent with ${\mathrm{TaO}}_{\text{x}}$ polyhedra with increased corner-sharing and reduced edge- and face-sharing structures.

Two-level systems (TLS) are an important, if not dominant, source of loss and noise for superconducting resonators such as those used in kinetic inductance detectors and some quantum information science platforms. They are similarly important for loss in photolithographically fabricated superconducting mm-wave/THz transmission lines. For both lumped-element and transmission-line structures, native amorphous surface oxide films are typically the sites of such TLS in nonmicrostripline geometries, while loss in the (usually amorphous) dielectric film itself usually dominates in microstriplines. We report here on the demonstration of low TLS loss at GHz frequencies in hydrogenated amorphous silicon (a-Si:H) films deposited by plasma-enhanced chemical vapor deposition in superconducting lumped-element resonators using parallel-plate capacitors (PPCs). The values we obtain from two recipes in different deposition machines, $7\times {10}^{-6}$ and $12\times {10}^{-6}$, improve on the best achieved in the literature by a factor of 2–4 for a-Si:H and are comparable to recent measurements of amorphous germanium. Moreover, we have taken care to extract the true zero-temperature, low-field loss tangent of these films, accounting for temperature and field saturation effects that can yield misleading results. Such robustly fabricated and characterized films render the use of PPCs with deposited amorphous films a viable architecture for superconducting resonators and they also promise extremely low loss and high quality factor for photolithographically fabricated superconducting mm-wave/THz transmission lines used in planar antennas and resonant filters.

Twisted bilayers of transition metal dichalcogenides (TMDs) have revealed a rich exciton landscape including hybrid excitons and spatially trapped moiré excitons that dominate the optical response of the material. Recent studies have shown that in the low-twist-angle regime, the lattice undergoes a significant relaxation in order to minimize local stacking energies. Here, large domains of low energy stacking configurations emerge, deforming the crystal lattices via strain and consequently impacting the electronic band structure. However, so far the direct impact of atomic reconstruction on the exciton energy landscape and the optical properties has not been well understood. Here, we apply a microscopic and material-specific approach and predict a significant change in the potential depth for moiré excitons in a reconstructed lattice, with the most drastic change occurring in naturally stacked TMD homobilayers. We show the appearance of multiple flat bands and a significant change in the position of trapping sites compared to the rigid lattice. Most importantly, we predict a multipeak structure emerging in optical absorption of ${\mathrm{WSe}}_2$ homobilayers—in contrast to the single peak that dominates the rigid lattice. This finding can be exploited as an unambiguous signature of atomic reconstruction in optical spectra of moiré excitons in naturally stacked twisted homobilayers.

Transition metal dichalcogenides are known for their intriguing spin-valley effects, which can be harnessed through proximity in van der Waals heterostructures. Their hexagonal monolayers exhibit significant Zeeman band splitting of valence bands, reaching up to several hundred meV and giving rise to spin textures that yield long spin lifetimes. However, this effect is suppressed in the hexagonal bilayers due to inversion symmetry. The recent discovery of sliding ferroelectricity in ${MX}_2$ bilayers ($M=\mathrm{Mo}$, W; $X=\mathrm{S}$, Se) opens a pathway for the electrical control of the spin properties in these materials. While substantial Zeeman splitting is found in the rhombohedral structure, its behavior during the ferroelectric transition remains unclear. In this paper, we explore different stacking configurations of ${MX}_2$ bilayers by sliding and demonstrate, using density functional theory calculations and symmetry analysis, that the Zeeman effect completely dominates the spin polarization of bands throughout the structural transition. This promises to maintain robust spin transport in polar ${MX}_2$ bilayers, opening potential avenues for ferroelectric spintronics.

Lithium niobate $\mathrm{LiNb}{\mathrm{O}}_3$ (LN) has emerged as a promising electro-optic (EO) material with applications in silicon photonics. It demonstrates a large linear EO response, often referred to as the Pockels effect. We report on a first-principles investigation of the origins of the Pockels response in $R3c$ LN. We examine three contributions to the Pockels tensor, its electronic, ionic (Raman), and piezoelectric components, and demonstrate that the large value of Raman susceptibility can be traced to specific $A_1$ modes that affect the Nb-O bonding. To examine the origin of the piezoelectric Pockels response, we compute the elasto-optic and piezoelectric tensors. Importantly, the largest component of the Pockels tensor $r_{33}$ is dominated by the ionic response, which explains the insensitivity of the EO effect in LN to frequency.

Lead halide hybrid perovskite single crystals have been grown using antisolvent vapor-assisted crystallization. The chemical composition and structural model of the crystals have been established using nuclear magnetic resonance and single crystal x-ray diffraction, leading to the formula $\mathrm{F}{\mathrm{A}}_{0.9}\mathrm{M}{\mathrm{A}}_{0.1}\mathrm{Pb}{\mathrm{I}}_{2.23}{\mathrm{Br}}_{0.77}$. The hexagonal crystallographic structure with $P{6}_3$/mmc space group has been confirmed by transmission electron microscope study. Through a detailed analysis of the single crystal XRD data, the locations of $\mathrm{F}{\mathrm{A}}^{+}$ and $\mathrm{M}{\mathrm{A}}^{+}$ in the unit cell have been identified, and the off-centering of ${\mathrm{Pb}}^{2+}$ on the octahedral sites has been unveiled, probably due to the Pauli repulsion of the lone pair. This material is a wide-gap semiconductor with $E_g$ = 2.27 eV and demonstrates photoluminescence activity. The thermal conductivity is disorder-dominated with an extremely low value of $0.17\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ from about 75 K up to 325 K. The present investigation on $\mathrm{F}{\mathrm{A}}_{0.9}\mathrm{M}{\mathrm{A}}_{0.1}\mathrm{Pb}{\mathrm{I}}_{2.23}{\mathrm{Br}}_{0.77}$ single crystal demonstrates that low values of thermal conductivities are obtained in this hexagonal family of hybrid halide perovskites, with mixed cationic and anionic disorder.

In diamond, nitrogen defects like the substitutional nitrogen defect $\left({\mathrm{N}}_{\mathrm{s}}\right)$ or the nitrogen-vacancy-hydrogen complex (NVH) outnumber the nitrogen-vacancy (NV) defect by at least one order of magnitude creating a dense spin bath. While neutral ${\mathrm{N}}_{\mathrm{s}}$ has an impact on the coherence of the NV spin state, the atomic structure of NVH reminds of a NV center decorated with a hydrogen atom. As a consequence, the formation of NVH centers could compete with that of NV centers possibly lowering the N-to-NV conversion efficiency in diamond grown with hydrogen-plasma-assisted chemical vapor deposition (CVD). Therefore, monitoring and controlling the spin bath is essential to produce and understand engineered diamond material with high NV concentrations for quantum applications. While the incorporation of ${\mathrm{N}}_{\mathrm{s}}$ in diamond has been investigated on the nano- and mesoscale for years, studies concerning the influence of CVD parameters and the crystal orientation on the NVH formation have been restricted to bulk N-doped diamond providing high-enough spin numbers for electron paramagnetic resonance and optical absorption spectroscopy techniques. Here, we investigate submicron-thick (100)-diamond layers with nitrogen contents of $(13.8\pm 1.6)\mathrm{ppm}$ and $(16.7\pm 3.6)\mathrm{ppm}$, and exploiting the NV centers in the layers as local nanosensors, we demonstrate the detection of ${}^{}{\mathrm{NVH}}^{-}$ centers using double electron-electron resonance (DEER). To determine the ${}^{}{\mathrm{NVH}}^{-}$ densities, we quantitatively fit the hyperfine structure of ${}^{}{\mathrm{NVH}}^{-}$ and confirm the results with the DEER method usually used for determining ${}^{}{{\mathrm{N}}_{\mathrm{s}}}^0$ densities. With our experiments, we access the spin bath composition on the nanoscale and enable a fast feedback loop in CVD recipe optimization with thin diamond layers instead of resource- and time-intensive bulk crystals. Furthermore, the quantification of ${}^{}{\mathrm{NVH}}^{-}$ plays a very important role for understanding the dynamics of vacancies and the incorporation of hydrogen into CVD diamond optimized for quantum technologies.