Oxygen scavenging at oxide heterointerfaces has emerged as a powerful route for stabilizing metastable phases that exhibit interesting phenomena, including high-mobility, two-dimensional electron gases and high-${\mathrm{T}}_c$ superconductivity. We investigate structural and chemical interactions at the heterointerface formed between Al or Eu and the charged-ordered insulator, ${\mathrm{BaBiO}}_3$, leading to emergent superconductivity at 6 K. A combination of x-ray diffraction and electron microscopy measurements shows that oxygen scavenging by the Eu and Al adlayers leads to the formation of superconducting intermetallic ${\mathrm{BaBi}}_3$ in nominal $\mathrm{Eu}\text{/}{\mathrm{BaBiO}}_3$ and $\mathrm{Al}\text{/}{\mathrm{BaBiO}}_3$ bilayers. Anisotropic magnetotransport measurements and current-voltage signatures of quasi-two-dimensional superconductivity are observed. The mechanisms behind quasi-two-dimensional superconductivity and the role of disorder remain to be clarified. These findings highlight the potential for the use of in situ reduction of bismuthate heterostructures as a platform for stabilizing materials with exotic functional properties. Additionally, the strong spin-orbit coupling at the Bi sites may pave the way for the realization of high-${\mathrm{T}}_c$ topological superconductivity.

Crystals with practical applications are constrained by a variety of requirements. To quickly pick up the candidates from a huge amount of structures, whether experimentally or theoretically, is always is longstanding pursuit. In this study, we use the booming machine learning (ML) technique to explore such a roadmap for nonlinear optical crystals. In consideration of lacking adequate data about the second-harmonic generation, we put the phase matching performance as one of the most primary requisites and screening materials with excellent phase matching traits as the first step. We train the ML model based on the graph neural networks, modeling crystal structures as atomic graphs, achieving a mean absolute percentage error $<5\%$ on the test set. By using the model to predict refractive indices both at 1064 nm and 532 nm, we screen out three moderate birefringence materials, ${\mathrm{H}}_4{\mathrm{CN}}_2\mathrm{O},{\mathrm{KBO}}_2$, and ${\mathrm{RbN}}_3$ from the Materials Project database and give out their phase matching condition. After the step, we employ the first-principles calculation to verify the candidate of nonlinear optical crystals for these three materials and find ${\mathrm{H}}_4{\mathrm{CN}}_2\mathrm{O}$ exhibiting second-harmonic generation response. Our study demonstrate a potential roadmap for a quick screening out of practical nonlinear optical crystals by using present ML methods under inadequate data specified on nonlinear optical crystals.

Two-dimensional (2D) magnetic materials are attracting significant interest due to their potential for exotic spin-dependent transport phenomena and spintronic applications. $\mathrm{FeP}{\mathrm{d}}_2\mathrm{T}{\mathrm{e}}_2$ is a layered ferromagnet with quasi-1D zigzag Fe chains and features intrinsic crystal twinning. Combining angle-dependent magnetotransport, magneto-optical Kerr effect imaging, and theoretical calculations, we establish a twin-domain-induced linkage between microstructure and transport. This intrinsic twinning generates a pseudo-fourfold in-plane magnetic anisotropy. Angle-dependent magnetoresistance (AMR) measurements confirm the presence of fourfold-symmetry components in the ferromagnetic state, while magneto-optical Kerr microscopy directly visualizes orthogonal in-plane magnetic domains that correspond to the twin structure. First-principles calculations suggest the anomalous Hall effect originates from an intrinsic Berry curvature mechanism, driven by strong spin-orbit coupling. The twinning strongly suppresses the measured in-plane anomalous Hall conductivity relative to single-domain expectations, indicating structural twinning as an effective microstructural knob for tuning Berry-phase responses. These results reveal a clear structure–property relationship in a low-symmetry layered magnet and position $\mathrm{FeP}{\mathrm{d}}_2\mathrm{T}{\mathrm{e}}_2$ as a platform for domain-engineered control of anisotropic magnetotransport in layered and low-dimensional ferromagnets.

In this work we present a systematic in-depth study of how we can alter the magnetotransport properties of magnetic topological insulator thin films by tuning the parameters of the molecular-beam epitaxy. First, we show how a varying substrate temperature changes the surface morphology and, when chosen properly, leads to a high crystal quality. Next, the effect of the chromium concentration on the film roughness and crystal quality is investigated. Finally, both the substrate temperature and the chromium concentration are investigated with respect to their effect on the magnetotransport properties of the magnetic topological insulator thin films. It becomes apparent that the substrate temperature and the chromium concentration can be used to tune the Fermi level of the film which allows to make the material intrinsically charge neutral. A very low chromium concentration furthermore allows to tune the magnetic topological insulator into a regime where strong superconducting correlations can be expected when combining the material with a superconductor.

Ternary alloys formed by adding transition metals scandium and yttrium to aluminum nitride have been shown to have enhanced ferroelectric and piezoelectric properties that enable new functional capabilities in electronic and optoelectronic devices. Moreover, incorporating boron into aluminum nitride can lead to a significant increase in the spontaneous polarization and strong ferroelectric properties. Although these alloys have been experimentally synthesized, their growth is particularly challenging. Furthermore, the differing crystal structures of the parent binary compounds lead to phase segregation phenomena that make it impossible to grow the alloys in one specific crystal modification over the entire composition range. As a result, there is a lack of understanding of the fundamental properties of these alloys, particularly regarding the piezoelectric characteristics. In this work, we employ a density functional theory-based approach to study the structural and elastic properties of these three alloys. We calculate the lattice constants, the internal parameter, and the Poisson's ratios for the full range of compositions in these alloys in order to identify where phase segregation may occur. Furthermore, we study their piezoelectric properties by first evaluating the spontaneous polarization and subsequently the piezoelectric stress and strain coefficients as a function of composition. To validate the theoretical model, we compare the calculated values with the experimental data available for some of the alloy compositions. Finally, we provide parametric expressions for the structural and piezoelectric properties, which can be used for device design.

The knowledge of the properties of americium oxides is crucial for nuclear fuel optimization and potential future use in radioisotope thermoelectric generators. In this paper, we used a combination of state-of-the-art complementary atomic scale modeling methods to determine the properties of the cubic phases of americium oxides. We used the Cooper-Rushton-Grimes (CRG) interatomic potential updated for the study of americium-bearing oxides to study the structural and thermodynamic properties of the cubic phases of americium oxides ${\mathrm{AmO}}_x$ with $1.5\le x\le 2$, i.e., from the sesquioxide C-${\text{Am}}_{\text{2}}{\text{O}}_3$ to the dioxide ${\text{AmO}}_{\text{2}}$, between 250 K and 4500 K. A large number of properties were calculated as a function of composition and temperature: cell parameter, thermal expansion coefficient, enthalpy increment and specific heat capacity. The results reproduce almost exactly the melting temperature of the sesquioxide and show a phase transition at high temperature for the ${\mathrm{AmO}}_{1.55}$ and ${\mathrm{AmO}}_{1.60}$ compounds, which could result in a phase observed experimentally for these O/M ratios. They also allow us to recover the only melting temperature reported for ${\text{AmO}}_{\text{2}}$ in literature but for a much lower O/M ratio, approximately around 1.55–1.60. The reduction of ${\text{AmO}}_{\text{2}}$ to ${\text{AmO}}_{\text{2-x}}$ in temperature cannot, however, be obtained using the CRG empirical potential formalism due to the fixed charge formalism. We therefore performed electronic structure calculations to determine the properties of ${\text{AmO}}_{\text{2}}$ in temperature up to around 3000 K using density functional theory in the $\mathrm{DFT}+U$ approximation and using a functional taking into account van der Waals interactions. The enthalpy increment and specific heat capacity obtained are in excellent agreement with the available measurements and calphad modeling. The formation of oxygen dimers separated from the crystal and the reduction of ${\text{AmO}}_{\text{2}}$ is observed, with the variation in O/M ratio as a function of temperature agreeing with the results of calphad calculations. The results presented in this paper provide significant insight into the properties of the cubic phases of americium oxides and complement the little experimental data on this system, especially at high temperature, and are now available to refine phase diagram calculations and fuel performance codes simulations.

Lithiation-assisted epitaxy offers a flexible and robust approach for synthesizing high-quality Li-containing materials and interfaces with precise control. In this study, we use lithium tungstate (${\mathrm{Li}}_x\mathrm{W}{\mathrm{O}}_{3+x/2}$, where $x=0$ to 2) as a model system to investigate the intertwined effects of Li out-diffusion-induced compositional changes and surface-diffusion-induced morphological changes. By systematically varying synthesis and processing conditions, we uncover their impact on lithium tungstate film formation. Comprehensive characterizations, including X-ray diffraction, atomic force microscopy, X-ray photoemission spectroscopy, and time-of-flight secondary ion mass spectrometry, reveal that low-temperature growth ($<{300}^{\circ }\mathrm{C}$) followed by high-temperature annealing yields continuous lithium tungstate films with significantly reduced surface roughness. In contrast, high-temperature deposition ($\ge {300}^{\circ }\mathrm{C}$) accelerates surface diffusion and Li out-diffusion, leading to island formation. Furthermore, in situ scanning transmission electron microscopy demonstrates the beam sensitivity of ${\mathrm{Li}}_2\mathrm{W}{\mathrm{O}}_4$ and reveals a phase transition from ${\mathrm{Li}}_2\mathrm{W}{\mathrm{O}}_4$ to $\mathrm{LiW}{\mathrm{O}}_{3.5}$ under prolonged electron beam exposure. These findings deepen our understanding of how to control the composition and morphology of Li-containing films, providing valuable insights for the design and integration of energy materials.

Antiferromagnets (AFMs) have emerged as crucial materials for spintronic technologies for their ability to host spin-dependent transport phenomena, despite their zero net magnetization. Their robustness against external magnetic fields and ultrafast spin dynamics make them ideal for efficient spin-charge interconversion. However, unlike ferromagnets, many details of spin transport mechanisms in AFMs remain unexplored. In this study, we theoretically investigate the enhancement of the spin Hall effect in AFM materials, with a focus on Mn-based binary alloys. By alloying MnPt with Ir (${\mathrm{MnPt}}_x{\mathrm{Ir}}_{1-x}$) or Pd (${\text{MnPt}}_x{\text{Pd}}_{1-x}$), we aim to elucidate the impact of tuning the Fermi energy and of changing the spin-orbit coupling strength on the spin Hall conductivity, and ultimately on the spin Hall angle (SHA). We show that lightly doping MnPt with Ir enhances the SHA from approximately 3% in pristine MnPt, as experimentally reported at room temperature, to nearly 12% under the same conditions. Building on these findings, we employ density-of-states and band-structure analyses to unravel the microscopic origin of this enhancement. Overall, our results highlight the potential of antiferromagnetic alloys for efficient spin-current generation and underscore their promise for advancing spintronic applications.

The ${\mathrm{GdFeO}}_3$-type perovskite antiferromagnet ${\mathrm{NaOsO}}_3$, calculated here to be altermagnetic for all three typical collinear antiferromagnetic orders, was suggested early on to be a Slater-type insulator, due in large part to its continuous metal-insulator transition and its small energy gap. Below the Néel temperature, the gap opens along with “weak magnetism”, accompanied by a sharp change in the magnetic susceptibility and resistivity. Without explicit correlation in the band structure calculation, and neglecting spin-orbit coupling (SOC), already a gap opens. Inclusion of a modest on-site Coulomb repulsion ($U\sim 1$ eV) is sufficient to eliminate a SOC-induced small band overlap, opening a gap similar to the experimentally observed gap of around 100 meV. Combined evidence supports the viewpoint that ${\mathrm{NaOsO}}_3$ lies in an unusual crossover region between Slater and Mott insulator. The unreported altermagnetism in ${\mathrm{NaOsO}}_3$ is demonstrated and its consequences are considered. The origin of the very weak magnetism has been investigated using a combination of ab initio calculations and symmetry analysis of the magnetic space group, confirming the origin lying in the Dzyaloshinskii-Moriya SOC buttressed by altermagnetic order. After determining the easy axis, our calculation leads to an Os spin canting angle of about $3^{\circ }$, accounting for the observed weak magnetism and sharp change in the susceptibility. The altermagnetism spin-split bands (up to $\sim 100$ meV) are accompanied by a chiral-split magnon spectrum in both acoustic and optical modes in the THz range, and lead to significant anomalous Hall conductivity upon hole doping.

Here we report a structural phase transition and its interplay with superconductivity in the suboxide ${\mathrm{La}}_5{\mathrm{Pb}}_3\mathrm{O}$. Upon cooling through $T_t=225\mathrm{K},{\mathrm{La}}_5{\mathrm{Pb}}_3\mathrm{O}$ transforms from a high-temperature $I4$/mcm to a low-temperature $P4$/ncc structure in which La-Pb dimerization along the $c$ axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical resistivity and specific heat. High-pressure electrical transport measurements reveal that hydrostatic pressure suppresses the structural transition and possibly induces superconductivity with a maximum superconducting temperature of 10 K. Density functional theory calculations show minimal changes in the electronic density of states and no gap opening at $E_F$ across $T_t$, suggesting that the transition is driven by bonding effects rather than Fermi surface instability. These findings establish ${\mathrm{La}}_5{\mathrm{Pb}}_3\mathrm{O}$ as a promising platform for exploring the interplay between weak structural transitions and superconductivity.

Glass ceramics are functional materials created through controlled crystallization of base glasses, combining properties of both glasses and ceramics. Typically with crystallinity below 0.9, their crystal sizes, from nanometers to micrometers, are governed by processing conditions and nucleating agents. Smaller crystals enhance optical transparency, while larger ones improve mechanical strength, making the optimization of this tradeoff a critical challenge in composition and process design. We address this challenge quantitatively using continuum-level multiphysics modeling for both electromagnetic wave propagation and material fracture, which generate guiding curves for optimal property selection. Integrating these models incorporating microstructure effects and experimental data where the chemistry is encoded, we establish a comprehensive composition-processing-microstructure-properties map. Crucially, the one-to-one mapping from the microstructure space to the performance enables a physics transfer approach, supporting data-driven glass development of glass ceramics with tailored optical and mechanical properties, for reduced experimental costs and accelerated processes of material design.

It has recently been discovered that vapor deposition of amorphous silicon onto a substrate held at an optimal temperature reduces the concentration of low-energy excitations that dominate the low-temperature thermal, acoustic, and dielectric properties of almost all amorphous dielectric materials by almost three orders of magnitude. Using a similar film deposition process, it has also been shown that numerous organic glasses formed directly from the vapor phase at an optimal substrate temperature show “ultrastable” properties of enhanced kinetic stability, high density, and low entropy. In order to investigate a proposed connection between ultrastability and a strong reduction of these excitations in such vapor-deposited glasses, we deposit ultrastable thin films of the organic glass 2TNATA—4,4′,4′′-Tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine—on ultra-high-$Q$ mechanical resonator substrates known as double-paddle oscillators (DPOs). The low-energy excitations, commonly and successfully modeled as a distribution of two-level tunneling systems, TLSs, are measured through internal friction and characterized by a tunneling strength $C$. The ultrastable character of the films is confirmed through conventional and flash differential scanning calorimetry, and after initial internal friction measurements of the ultrastable state, the films were annealed into the ordinary state to quantify the difference in $C$. We find the ultrastable glasses to have $C\approx 6.8\times {10}^{-4}$, still within the glassy range, and representing a modest 25% reduction compared to the ordinary glass.

We investigate the shift current in two-dimensional (2D) Janus transition-metal dichalcogenides (TMDs). The shift current is evaluated using a real-time approach, where the coupling with an external field is described in terms of a dynamical Berry phase. This methodology incorporates electron-hole interactions and quasiparticle band structure renormalization through an effective Hamiltonian derived from many-body perturbation theory. We find that the shift current is strongly enhanced in correspondence with $C$ excitons. An analysis in terms of the electron-hole pairs reveals that electron and hole are localized on different atoms and thus, following an optical excitation, the center of the electron charge is displaced, giving rise to a significant photocurrent. Janus TMDs, with their intrinsic out-of-plane asymmetry and tunable electronic properties, are particularly appealing for next-generation optoelectronic and energy-harvesting technologies. These results highlight the role of excitons in the shift-current response of Janus TMDs and demonstrate their potential as promising building blocks for future photovoltaic devices.

The anharmonic behavior of phonons and thermal expansion of hexagonal zinc were studied from 15 to 690 K by inelastic neutron scattering (INS) and ab initio simulations. Phonon spectra were measured for $Q$-points covering the full Brillouin zone, giving the phonon density of states (DOS) and dispersions along high-symmetry directions. The dispersions were sharp at 15 K, but diffuse intensity was observed at energies above them. The dispersions broadened with temperature $T$ and the diffuse intensity became stronger. This diffuse intensity appeared in all INS measurements and simulations, except for classical molecular dynamics at 15 K. The temperature-dependent effective potential (TDEP) method, which included the nuclear quantum effect from zero-point vibrational dynamics, was used to calculate the free energy and thermal expansion. For $T<100\mathrm{K}$ nuclear quantum effects were essential for obtaining the correct negative thermal expansion, and path integral molecular dynamics (PIMD) was particularly effective for obtaining the negative thermal expansion in the basal plane. A Heisenberg-Langevin model for interacting phonons coupled to a thermal bath was able to reproduce the shape and intensity of the diffuse spectral features.