${\mathrm{LiGa}}_5{\mathrm{O}}_8$ in a spinel-type structure has recently been claimed to be an unintentional $p$-type ultra-wide-band-gap oxide semiconductor. While previous computational work did not yet identify the origin of $p$-type doping and in fact predicted insulating behavior by compensation of deep acceptors by shallow donors, defect characterization in terms of its optical signatures remains important. Rather than focusing on thermodynamic transition levels, as in earlier work, this present paper focuses on the vertical transitions in a defect configuration diagram of defects in different charge states, representing absorption and emission processes involving carrier capture/emission from/to band edges. In addition, the structural relaxation of several native defects is revisited by allowing for more complex symmetry breaking distortions in an effort to reconcile conflicting results in the previous literature. Special attention is given to the Li vacancy because it is the shallowest native acceptor. For this defect, the previously reported transition levels are revised on the basis of symmetry breaking relaxations. The calculated optical transition energies are also compared with a representative depth-resolved cathodoluminescence spectrum of a mist-CVD-grown ${\mathrm{LiGa}}_5{\mathrm{O}}_8$ film. Finally, we also study carbon impurities, which may become relevant for identifying carbon-related defects in MOCVD-grown ${\mathrm{LiGa}}_5{\mathrm{O}}_8$ materials.

We present a comprehensive study on the sputtering behavior of tungsten fuzz structures under deuterium and argon ion bombardment using three-dimensional simulations. We employed SDTrimSP-3D to investigate porosity as a predictor for the sputtering behavior, complementary to the well-established effects of surface roughness, with simulations conducted across multiple ion energies ($500\mathrm{eV}–2000\mathrm{eV}$) and incidence angles ($0^{\circ }-{85}^{\circ }$). Fuzz structures were algorithmically generated with varying porosities, and sputter yields were systematically calculated. The findings reveal a universal linear relationship between sputter yield and porosity/volume filling, demonstrating that porosity significantly suppresses sputtering. Importantly, the zero-porosity limit is given by the sputter yield of a rough, but solid surface rather than a flat target. This linear behavior holds consistently across the different ion types and energies for a wide range of incidence angles. When normalized to the rough-surface sputter yield, the slope of the porosity dependence is nearly constant, indicating a common underlying suppression mechanism. The study enhances fundamental understanding of sputtering in porous nanostructures and provides a simple, predictive framework with implications for material design, particularly in nuclear fusion research, where erosion of tungsten fuzz impacts reactor component lifetimes.

Nonlinear optical phenomena induced by ultra-fast lasers in two-dimensional (2D) materials have recently attracted significant research interest. Herein, we investigate monolayer bismuthene using first-principles simulation based on the real-time Time-Dependent Density Functional Theory (rt-TDDFT). The results indicate that it exhibits a pronounced optical Kerr effect, with a negative nonlinear refractive index (NNRI) $n_2=-1.194\times {10}^{-9}{\mathrm{cm}}^2/\mathrm{W}$, whose absolute value is comparable to that of typical two-dimensional materials. By analyzing the electron transition probabilities among the conduction band minimum (CBM), valence band maximum (VBM), and $\mathrm{VBM}+1$, combined with perturbation theory for multi-level problems, we attribute the NNRI to the competition between two-level and three-level processes. This study clarifies the microscopic origin of NNRI in monolayer bismuthene, laying a theoretical foundation for unraveling the nonlinear optical regulation law of elemental two-dimensional bismuth-based nanomaterials.

The atomic structure of $\gamma$-alumina, a metastable oxide central to applications ranging from heterogeneous catalysis to energy conversion and environmental remediation, has remained elusive for decades. This persistent uncertainty arises from the high concentration of aluminum vacancies and the difficulty of determining precise cation occupancy within the oxygen sublattice. Here, we address this challenge by combining aberration-corrected scanning transmission electron microscopy combined with ultrahigh-sensitivity energy-dispersive spectroscopy to investigate $\gamma {\text{-Al}}_2{\text{O}}_3$ formed during high-temperature oxidation of NiAl alloys. By integrating atomic-resolution imaging, elemental mapping, diffraction analysis, and density functional theory calculations, we identify a spinel-type $\gamma {\text{-Al}}_2{\text{O}}_3$ structure featuring a cubic close-packed oxygen framework, in which Al cations exclusively occupy octahedral interstitial sites. This site-selective occupancy leads to ordered distribution of aluminum vacancies, resolving a long-standing structural ambiguity regarding cation distribution in $\gamma {\text{-Al}}_2{\text{O}}_3$. Comparison with previous studies of hydroxide-derived $\gamma {\text{-Al}}_2{\text{O}}_3$ further reveals that the local structure of this metastable oxide is highly sensitive to synthesis pathway, precursor chemistry, and kinetic equilibration history. These results provide direct atomic-level insight into defect ordering and cation topology in $\gamma {\text{-Al}}_2{\text{O}}_3$, with implications for ion transport, catalytic activity, and thermal stability in alumina-based materials.

We successfully synthesized $\left[\mathrm{Co}{\left(m\text{−}\mathrm{Py}\text{−}\mathrm{V}\right)}_3{\left({\mathrm{NO}}_3\right)}_2\right]$, in which a ${\mathrm{Co}}^{2+}$ ion adopts a seven-coordinate pentagonal bipyramidal (PBP) geometry. Molecular orbital calculations reveal that one of the three verdazyl radicals in the molecule forms a nonmagnetic singlet dimer through the strong intermolecular interaction, leading to a triangular spin necklace composed of the remaining spin-1/2 radicals and a spin-3/2 ${\mathrm{Co}}^{2+}$ ion. Magnetic susceptibility and specific heat measurements reveal contributions from ferromagnetic and antiferromagnetic exchange interactions, as well as a low-temperature phase transition. Electron spin resonance spectra and magnetization curves are consistently explained using a simplified model that treats the system as an anisotropic $S=3/2$ monomer coupled to an isotropic $s=1/2$ chain. Our results demonstrate that introducing PBP-coordinated transition-metal centers into radical-based complexes provides an effective route to incorporating strong magnetic anisotropy into designed quantum spin models, establishing a versatile platform for exploring frustrated and anisotropic triangular spin necklaces.

Molecular beam epitaxy (MBE) is renowned for its potential for atomic layer control, but unexpected growth mechanisms can potentially compromise this level of precision. In this study, we employ first-principles calculations to investigate the atomistic processes governing the MBE growth of perovskite ${\mathrm{SrTiO}}_3$ and Ruddlesden-Popper ${\mathrm{Sr}}_2{\mathrm{TiO}}_4$ films on a ${\mathrm{SrTiO}}_3$ substrate. We systematically explore the potential molecular species in the gas phase and their reactions and diffusion dynamics on the film surfaces and layer edges. Our analyses uncover three mechanisms of importance for understanding this type of growth. First, oxygen vacancies can be dynamically induced during surface diffusion on defect-free substrate and noticeably accelerate the diffusion processes. Second, while the SrO layer is expected to grow in a single-layer growth mode, the presence of potential ${\mathrm{Ti}}_{\mathrm{Sr}}$ defects may promote the formation of SrO islands. Lastly, adsorbed Ti atoms and ${\mathrm{TiO}}_2$ molecules on the SrO bilayer can insert into SrO bilayers, resulting in an unexpected growth sequence. These findings may have broader implications for the MBE growth of metal oxide films and provide guidance for achieving improved control over their growth processes.

We investigate spacer-mediated long-range Dzyaloshinskii-Moriya interaction (LR-DMI) in $\mathrm{Co}/\mathrm{Cu}\left(n\right)/\text{HM}$ multilayers $(\text{HM}=\text{Pt}, \mathrm{Pd}, \mathrm{Ir}, \mathrm{W}, \mathrm{Mo})$ using first-principles calculations and micromagnetic simulations. LR-DMI shows a pronounced nonmonotonic, oscillatory dependence on Cu thickness, demonstrating that the intralayer DMI within Co can be tuned through a nonmagnetic spacer and a remote heavy-metal (HM) spin-orbit source. Atomic layer decomposition reveals that the LR-DMI signal is carried predominantly by the Co planes, and the heavy-metal overlayer acts as the spin-orbit source whose influence is transmitted through the Cu spacer and weakens with increasing $n$. Thickness-dependent electronic structure and charge density difference analyses link the oscillatory LR-DMI to spacer-tuned Co-Pt coupling and interface to interface charge redistribution that becomes progressively localized at larger $n$. Extending to different heavy-metal overlayers, all systems retain the same thickness-driven oscillatory backbone, while the amplitude and phase depend strongly on the heavy-metal species, consistent with $d$ band filling and relativistic character. Micromagnetic simulations for Pt and Ir stacks demonstrate that these first-principles LR-DMI trends translate into distinct field tunable skyrmion diameters and hysteresis behavior. These results establish a Co/HM1/HM2-type route for engineering single-layer DMI through nonmagnetic spacer and spin-orbit layers.

Transition-metal doping enables the introduction of spin functionality into halide double perovskites, while simultaneously modifying optical properties. Here, we combine controlled single-crystal growth, optical characterization, comprehensive electron paramagnetic resonance (EPR) spectroscopy, and first-principles modeling to identify the microscopic nature of Fe-related centers in Fe-doped ${\mathrm{Cs}}_2{\mathrm{AgBiBr}}_6$. Single crystals with nominal $\mathrm{F}{\mathrm{e}}^{3+}$ concentrations up to 15% in the precursor stage were grown using a controlled-cooling method, yielding reproducible Fe incorporation up to 0.1% with respect to Bi, without secondary phases. Despite this low concentration, Fe doping introduces electronic states that influence optical absorption and photoluminescence. EPR measurements reveal an S = 5/2 $\mathrm{F}{\mathrm{e}}^{3+}$-related center whose anisotropy follows the cubic-to-tetragonal phase transition below 120 K. Angular-dependent EPR resolves two configurations of this nearly axial spin center, with principal axes rotated by 90° and aligned with the a/b plane of the tetragonal lattice. Density-functional calculations attribute these centers to impurity-vacancy complexes, most likely ${\mathrm{Fe}}_{\mathrm{Bi}}\text{−}{\mathrm{V}}_{\mathrm{Br}}$, that stabilize in a basal configuration of the low-temperature phase. This approach resolves vacancy-coupled defect orientations, narrowing possible models to $\mathrm{F}{\mathrm{e}}^{3+}$-vacancy complexes and establishing them as stable, orientation-sensitive spin probes of structural symmetry in halide double perovskites, while providing a microscopic basis for tuning their magnetic and optical responses.

In this work, we provide high-precision thermal characterizations of $\beta \text{-G}{\mathrm{a}}_2{\mathrm{O}}_3$ single crystals across six crystallographic orientations ([001], [010], [100], [012], $\left[\overline{2}01\right]$, and $\left[\overline{1}02\right]$) using time-domain thermoreflectance (TDTR). Our measurements reveal a pronounced anisotropic thermal conductivity. Beyond establishing the benchmark values for bulk conductivity, we report a significant frequency dependence in the measured thermal conductivity that is primarily governed by the $\mathrm{transducer}/\beta \text{-G}{\mathrm{a}}_2{\mathrm{O}}_3$ interface. By varying transducer configurations, we demonstrate that this frequency dependence in TDTR measurements is not an intrinsic bulk characteristic but is instead governed by the boundary conditions at the interface. These findings resolve long-standing discrepancies in reported $\beta \text{-G}{\mathrm{a}}_2{\mathrm{O}}_3$ thermal conductivity data, offering a clearer framework for the thermal design of ultrawide bandgap devices.

${\mathrm{NiZr}}_2$ is a member of the transition metal (Tr) zirconide ${Tr\mathrm{Zr}}_2$ superconductor family having a ${\mathrm{CuAl}}_2$-type tetragonal structure. In this study, we report on two different pressure-induced properties of ${\mathrm{NiZr}}_2$. The first one is pressure-enhanced superconductivity; the transition temperature $\left(T_{\mathrm{c}}\right)$ reaches 4.8 K at $P=64.9$ GPa, while the $T_{\mathrm{c}}$ of ${\mathrm{NiZr}}_2$ at ambient pressure is lower than 2 K. From the calculated density of states (DOS) at the Fermi energy, we suggest that the enhancement of $T_{\mathrm{c}}$ cannot be explained by the change in DOS. The Debye temperature estimated from the resistance analysis increases with pressure, which suggests the possible correlation with the enhancement of superconductivity, while the $T_{\mathrm{c}}$ under pressure calculated based on a conventional model suggests that the conventional pairing is not sufficient to explain the pressure-enhanced $T_{\mathrm{c}}$. The second property is pressure-induced uniaxial negative thermal expansion (NTE). We performed synchrotron x-ray diffraction (XRD) under pressure at variable temperatures. From the temperature-dependent XRD patterns and the Rietveld refinement results, we confirmed the emergence of NTE along the $c$-axis in ${\mathrm{NiZr}}_2$. Since the NTE is one of the new functionalities in ${Tr\mathrm{Zr}}_2$, the pressure-induced NTE will be one of the important parts for developing new NTE materials and understanding the mechanism of NTE in the family and related materials.

Zinc oxide (ZnO) is a prototypical wide-band-gap semiconductor whose $n$-type conductivity can be tailored through extrinsic donor doping. However, the roles of defect association, compensation, and dopant mobility remain incompletely understood. We investigate Cl- and F-related defects in ZnO using screened hybrid density-functional calculations, with emphasis on substitutional donors, defect complexes, vacancy-mediated migration, and self-consistent carrier statistics. Substitutional chlorine and fluorine on the oxygen site, ${\mathrm{Cl}}_{\mathrm{O}}$ and ${\mathrm{F}}_{\mathrm{O}}$, are predicted to be shallow donors, with (+/0) transition levels above the conduction-band minimum and low formation energies under O-poor conditions. Halogen-native-defect complexes can be thermodynamically bound and provide possible compensation or passivation channels, but their impact on the carrier concentration depends on their equilibrium abundance and charge-state distribution. Self-consistent charge-neutrality calculations show that both Cl and F substitutional donors can sustain $n$-type conditions under the freeze-in treatment considered here, with the charge balance dominated by ionized substitutional donors and free electrons. Large vacancy-mediated migration barriers further indicate that substitutional halogen donors are kinetically stable after incorporation. These results provide a microscopic description of the thermodynamic, electronic, and kinetic factors governing Cl and F doping in ZnO.

Discontinuous shear thickening (DST) in dense suspensions leads to flow instabilities that limit processing in a wide range of industrial and natural systems. Although high-power ultrasound has long been known to fluidize these materials, the physical origin of this effect remains unclear. Here, we investigate adhesive cornstarch suspensions, in which DST emerges from fragile load-bearing force networks embedded within heterogeneous density-wave structures. Using a rheo-ultrasound setup, where high-power ultrasound is superimposed onto a constant shear-rate flow, we demonstrate that ultrasound does not suppress shear thickening but continuously shifts the DST transition toward higher shear rates, thereby reducing the apparent viscosity. This shift is evidenced by the collapse of stress probability distributions measured at different ultrasound amplitudes onto master curves, revealing a renormalization of the shear thickening transition. We interpret these results within a separation-of-timescales framework. Because the acoustic oscillation period is much shorter than the characteristic timescale of suspension restructuring, the suspension structure can be considered quasistatic on the acoustic timescale, while ultrasound generates high-frequency oscillatory interstitial flows that perturb the local hydrodynamic stresses within the force-network structure. Guided by scaling analysis and estimates of the relevant physical stresses and timescales, we show that several microscopic mechanisms—including ultrasound-induced boundary slip, localized acoustic streaming, and pore-scale hydrodynamic fluctuations that destabilize force networks—are compatible with the observed experimental results. These findings provide a physical framework for understanding acoustic control of shear thickening in adhesive dense suspensions and establish ultrasound as a promising strategy for controlling discontinuous shear thickening and associated flow instabilities.

Pyrite-structure iron disulfide, in addition to being an important mineral, is also an $\sim 1$-eV-band-gap semiconductor with substantial application potential. In particular, pyrite's earth-abundant, nontoxic, low-cost constituents, combined with its high visible light absorption, high carrier mobility, good minority carrier diffusion length, and other attributes, have led to it being pursued as a photovoltaic absorber material. An effort in this direction from the 1980s was not particularly successful, however, with pyrite-based solar cells not exceeding $\sim 3\%$ power conversion efficiency. Subsequent to that effort, increased focus on sustainable energy technologies drove a substantial resurgence of interest in ${\mathrm{FeS}}_2$, more closely focused on the fundamental obstacles to high performance as a photovoltaic absorber. This second wave of effort took place over the last 15 years or so, quite strongly focused on high-quality ${\mathrm{FeS}}_2$ single crystals as model systems. This Research Update aims to summarize the knowledge and understanding gained through this recent effort, focusing specifically on the electronic (mostly transport) properties of single-crystal pyrite. Highlighted advances include comprehensive study of surface conduction in ${\mathrm{FeS}}_2$, greatly improved understanding of doping, and consequent deeper insight into fundamental behavior such as conduction mechanisms, the insulator-metal transition, and doping-induced magnetism. Through such advances, substantial insights into the origins of the underperformance of pyrite ${\mathrm{FeS}}_2$ as a photovoltaic material have been obtained, to the point that fresh strategies for redesigned solar (and other) devices mitigating these problems can now be formulated and tested.

Alloys based on the Cu-Ag-Co system are of significant technological and scientific interest due to the limited mutual solubility of all three elements, which leads to complex microstructural behavior. In this work, we present the new classical interatomic potential for this system that accurately reproduces basic thermodynamic and kinetic properties, achieving an accuracy comparable to that of modern machine learning interatomic models. The potential is formulated in a classical functional form, which provides high computational efficiency and makes it well-suited for large-scale molecular dynamics simulations. As an example of application, we investigate atomic diffusion and precipitation in Cu-Ag-Co alloys. The model reproduces key trends in both self- and impurity diffusion, including the inverse correlation between diffusivity and melting temperature and the strong suppression of Co diffusion in the considered metals.

Coherent crystalline interfaces form when a pair of joined crystals share lattice sites. Such interfaces are ubiquitous in materials, minerals, and compounds, with examples including grain boundaries in polycrystals and phase boundaries in multiphase systems. Existing methodologies such as the topological model [R. C. Pond, X. Ma, Y. W. Chai, and J. P. Hirth, Topological modelling of martensitic transformations, in Dislocations in Solids Vol. 13, edited by F. R. N. Nabarro and J. P. Hirth (Elsevier, Amsterdam, 2007),  Chap. 74, pp. 225–261] provide a framework for understanding the nature of coherency between two crystals and the line defect content within an interface. However, these methods only consider states of coherency achieved via affine transformations. Here we show that in some interfaces, local relaxations in the form of nonaffine transformations lead to the introduction of additional coincidence sites within the interface; we term this class of interfaces e-coherent. These nonaffine relaxations are topologically equivalent to inserting disconnection (or disclination) dipoles or loops into the interface. Unlike traditional interfacial line defects, the defects associated with e-coherency cannot have long-range stress fields, and their motion alters the state of coherency between the crystals. Given these unique properties, we differentiate them from other defects by referring to them as discohesions. Through atomistic simulations and transmission electron microscopy, we show that the energetics and kinetics of e-coherent interfaces are strongly affected by the discohesion content in the interface, leading to fundamentally different behavior compared with non-e-coherent interfaces. We demonstrate that e-coherency occurs in grain, twin, and phase boundaries and that a given interface can have multiple possible e-coherent states. These results suggest that e-coherency is likely to be pervasive in crystalline solids.

Machine-learning models in physical sciences often assume that complex emergent properties can be predicted using a single homogeneous inference task. However, many physical phenomena are intrinsically conditional, involving distinct processes governing phase feasibility and physical-property optimization. Here we show that superconductivity prediction is more naturally formulated as a hierarchical inference problem in which superconducting feasibility and critical-temperature $\left(T_{\mathrm{c}}\right)$ optimization are represented by a shared descriptor space with task-dependent reweighting. Using a balanced dataset of more than 26 000 inorganic materials comprising both superconductors and nonsuperconductors, we demonstrate that superconducting feasibility is primarily controlled by an electronic–compositional backbone, whereas achievable $T_{\mathrm{c}}$ depends on additional structural and magnetic/orbital effects. Guided by this decomposition, we construct a physics-aligned hierarchical learning framework that first predicts superconducting feasibility using the electronic–compositional backbone and subsequently predicts $T_{\mathrm{c}}$ using an expanded descriptor set. Feature clustering and Shapley additive explanation-based attribution further show that the electronic–compositional backbone provides a minimal dominant representation of feasibility, while additional descriptor groups modulate achievable $T_{\mathrm{c}}$ through constraint and context-dependent effects. The two-stage framework reduces end-to-end $T_{\mathrm{c}}$ prediction error by explicitly accounting for the conditional nature of superconductivity. These results establish superconductivity prediction as a hierarchically structured problem and provide a physically interpretable bridge between data-driven discovery and first-principles modeling, defining a sequential design principle for superconductor discovery. More broadly, the results show that physically interpretable machine-learning behavior can emerge from hierarchical organization and conditional reweighting within descriptor space rather than from increasingly complex model architectures.