By resorting to first-principles simulations, we unveil the existence of peculiar electronic states in non-stoichiometric amorphous SiN that seem to float in the internal cavities present in the system. These states, if unoccupied, are located in the conduction band along with regular antibonding states. Upon occupation by electrons, they are energetically displaced in the gap of the system or in the upper part of the valence band depending on the stoichiometry and morphology of the cavities, without significant change in their floating nature. These localized floating states are not bound to any specific atom and can be easily charged/uncharged providing insight into the mechanism responsible for the basic function of flash memory devices and guidelines for their design.

Intermetallic compounds containing transition metals and group III-V metals tend to possess strong correlations and high catalytic activities, both of which can be enhanced via reduced dimensionality. Nanostructuring is an effective approach to explore this possibility, yet the synthesis of nanostructured intermetallics is challenging due to vast differences in melting points and vapor pressures of the constituent elements. In this work, we demonstrate that this challenge can be overcome with thermomechanical nanomolding (TMNM), exemplified by the synthesis of intermetallic ${\mathrm{CoIn}}_3$ and ${\mathrm{RhIn}}_3$ nanowires. We show that TMNM successfully extrudes single-crystalline nanowires of these compounds down to the 20-nm diameter range, and the nanowires remain metallic with resistivity values higher than calculated bulk resistivity. We discuss possible effects of surface roughness scattering, vacancy-induced scattering, and surface oxidation, on the measured resistivities of the nanowires. For ${\mathrm{CoIn}}_3$ nanowires, the measured resistivity values are the first reported values for this compound.

Construction of transferable machine-learning interatomic potentials with a minimal number of parameters is important for their general applicability. Here, we present a machine-learning interatomic potential with the functional form of the bond-order potential for comprehensive exploration over the configuration space of carbon. The physics-based design of this potential enables robust and accurate description over a wide range of the potential energy surface with a small number of parameters. We demonstrate the versatility of this potential through validations across various tasks, including phonon dispersion calculations, global structure searches for clusters, phase diagram calculations, and enthalpy-volume mappings of local minima structures. We expect that this potential can contribute to the discovery of novel carbon materials.

We report the excitonic properties of hexagonal boron-nitride (h-BN) thin films as a function of thickness using deep-ultraviolet photoluminescence spectroscopy and spectroscopic ellipsometry for optical absorption analysis. The peak positions of the defect-induced donor-acceptor PL emissions and the band-to-band exciton absorption exhibit a blueshift with increasing thickness or an increase in the effective dielectric constant of the surrounding environment. The optical absorption spectra analyzed using the Elliott model, combined with renormalized band-gap calculations, reveal an exciton binding energy of 1.04 eV for monolayer h-BN, which decreases to 0.16 eV in h-BN single crystal due to environmental screening effects on the electron-hole interactions. Furthermore, both the band-gap value and Urbach energy decrease as the film thickness increases. The optical absorption coefficient derived from spectroscopic ellipsometry measurement of monolayer h-BN is directly compared with results from the first-principles GW plus Bethe-Salpeter equation calculations.

We measure radiative and nonradiative rates for two sets of size-purified colloidal silicon nanocrystals (SiNCs) with overlapping size distributions but different quantum yields (QYs). Plasma-synthesized SiNCs of two distinct targeted diameters are processed into monodisperse fractions through density-gradient ultracentrifugation in organic solvents, where the nanocrystals are shielded from air throughout synthesis, passivation, and purification. At a common nanocrystal diameter, fractions from the smaller, lower-QY parent exhibit lower QY and lower photoluminescence lifetime than fractions from the larger, higher-QY parent, and a simple scaling argument is used to link this effect to differences in the density of surface quenching sites. In contrast, both sets of fractions exhibit the same radiative rate, which we suggest is a strong signature of core emission. Our results reveal steep changes in the nonradiative rate with changes in nanocrystal size and surface chemistry.

MXenes, a growing family of two-dimensional transition metal carbides and nitrides, have demonstrated substantial potential for terahertz (THz) electromagnetic interference (EMI) shielding. The adjustable and high electrical conductivity of titanium carbide, coupled with its absorption capabilities in the THz range, is utilized in the development of electrochemically and optically controlled devices, making them ideal for dynamic EMI shielding control. The sufficient EMI shielding effectiveness (SE) of $2.5\times {10}^4\mathrm{dB}{\mathrm{g}}^{-1}{\mathrm{cm}}^2$ can be enhanced through electrochemical doping, reaching levels as high as $4\times {10}^4\mathrm{dB}{\mathrm{g}}^{-1}{\mathrm{cm}}^2$ (at $+2\text{V}$). Furthermore, this initial EMI shielding can be improved by increasing the thickness, achieving an SE of 27 dB. With ultrafast optical pulses at 800 nm, tunability is achieved through a novel photoinduced enhancement in transparency, a phenomenon known as negative photoconductivity. A micron-thick film exhibits a long-lived photoinduced change in SE of $-0.25\text{dB}$. Our research enables the advancement of adaptable electromagnetic interference shielding components, which are ideally suited for the design and fabrication of innovative THz devices, including highly responsive detectors with both optical and electrical control capabilities.

X-ray photoelectron spectroscopy (XPS) is used to determine the energy levels associated with the ${\mathrm{Co}}^{2+/3+}$ and ${\mathrm{Fe}}^{2+/3+}$ charge transition levels in ${(\mathrm{La},\mathrm{Sr})\mathrm{CoO}}_{3-\delta }$ and ${(\mathrm{La},\mathrm{Sr})\mathrm{FeO}}_{3-\delta }$, respectively. The charge transition levels are revealed by varying the Fermi level by means of oxidizing and reducing treatments. The ${\mathrm{Co}}^{2+/3+}$ transition occurs at $0.15\pm 0.05\mathrm{eV}$ above the valence band maximum of ${(\mathrm{La},\mathrm{Sr})\mathrm{CoO}}_{3-\delta }$ and the ${\mathrm{Fe}}^{2+/3+}$ transition at $1.25\pm 0.05\mathrm{eV}$ above the valence band maximum of ${(\mathrm{La},\mathrm{Sr})\mathrm{FeO}}_{3-\delta }$, respectively. In combination with the energy band alignment determined from XPS analysis in the course of interface formation, it is derived that the energetic difference of the charge transition levels coincides with that in Co-doped ${\mathrm{BiFeO}}_3$, suggesting transferability of the energy levels in perovskite-type materials. The difference in charge transition levels directly relates to the easier reduction of Co compared to Fe. The result emphasizes that the oxidation states of Fe and Co in mixed compounds must be treated independently for a quantitative description of (defect) properties. They also provide a natural direct explanation for the higher electronic conductivity of ${(\mathrm{La},\mathrm{Sr})\mathrm{CoO}}_{3-\delta }$ compared to that of ${(\mathrm{La},\mathrm{Sr})\mathrm{FeO}}_{3-\delta }$, and for the acceptor behavior of Co in ${(\mathrm{La},\mathrm{Sr})\mathrm{FeO}}_{3-\delta }$.

At ambient conditions, the high-entropy alloy superconductor $\mathrm{R}{\mathrm{e}}_{0.6}{\left(\mathrm{NbTiZrHf}\right)}_{0.4}$ exhibits exceptional mechanical properties among high-entropy alloys, with its hexagonal phase achieving nanoindentation hardness of 18.5 GPa. We report on a unique pressure-induced structural transformation from a hexagonal phase to a body-centered cubic (BCC) phase, revealed by synchrotron x-ray diffraction measurements up to 70 GPa. This first-order transition, accompanied by a 6.1% volume collapse, occurs at 44 GPa and results in a BCC structure with random site occupancy by the five constituent elements, which is remarkably retained upon decompression to ambient conditions. The transformation proceeds via a martensiticlike, diffusionless mechanism without elemental segregation, enabled by pressure-induced electronic redistribution and atomic-scale disorder. These findings demonstrate a rare case of metastable phase retention in a chemically complex alloy and offer new insights into structure-stability relationships under pressure.

Three-dimensional quantum spin liquids have remained elusive, hindered by reduced quantum fluctuations from larger lattice connectivity inherent to high-dimensional systems. Here, we investigate the remarkable persistence of dynamical short-range magnetic correlations in the nearly body-centered cubic garnet ${\mathrm{NaCa}}_2{\mathrm{Cu}}_2{\left({\mathrm{VO}}_4\right)}_3$ down to $T=50\mathrm{m}\mathrm{K}$, two orders of magnitude below its Curie-Weiss temperature. Using a combination of neutron and muon spectroscopies plus numerical simulations, we demonstrate that a dynamical regime emerges, characterized by a dual response in the inelastic spectrum composed of short-live dispersive excitations and a quasielastic component. Strongly frustrated exchange interactions combined with subtle temperature-dependent Jahn-Teller spin-lattice effects are a plausible mechanism to explain the origin of this spin-liquid behavior.

Magnetic thin films with strong magnetoelastic coupling and low Gilbert damping are key materials for many magnetoelectric devices. Here, we investigated the effects of boron doping concentration on magnetostriction and temperature dependent Gilbert damping in magnetron sputtered ${\left({\mathrm{Fe}}_{80}{\mathrm{Ga}}_{20}\right)}_{1-x}{\mathrm{B}}_x$ films. A crystalline to amorphous structural transition was observed for a boron content near 8% and coincided with a decrease in coercivity from 76 Oe to 3 Oe. A 10% doping concentration is optimal for achieving both large magnetostriction of 48.8 ppm and low Gilbert damping of $6\times {10}^{-3}$. The temperature dependence of the damping shows an increase at low temperatures with a peak around 40 K, and we associate the relative increase $\mathrm{\Delta }\alpha /{\alpha }_{\mathrm{RT}}$ with magnetoelastic contributions to the damping, which has a maximum of 55.7% at 8% boron. An increase in the inhomogeneous linewidth broadening was observed in the structural transition regime at about 8% boron concentration. This study suggests that incorporation of glass forming elements, in this case boron, into ${\mathrm{Fe}}_{80}{\mathrm{Ga}}_{20}$ is a practical pathway for simultaneously achieving enhanced magnetoelastic coupling and reduced Gilbert damping.

A newly identified class of magnetic materials called altermagnets has attracted much attention due to the practical properties of spin-splitting bands akin to ferromagnets and small compensated magnetization akin to antiferromagnets. These features make them promising candidates for applications in spintronics devices. Among candidate materials, CrSb is promising because of its high ordering temperature (∼705 K) and large spin-splitting energy; however, it is predicted that tuning the Néel vector requires additional symmetry breaking or a change in the easy magnetization axis. While applying epitaxial strain can modulate the symmetry, the selection of substrates with closely matched lattice constants for heteroepitaxial growth is limited for altermagnets, which generally have low crystal symmetry. Therefore, exploring the heteroepitaxial growth of altermagnet thin films on well-established but dissimilar crystal systems is valuable. (001)-oriented III-V semiconductors, which share group-V elements with the overgrown CrSb, offer an ideal platform because they are expected to have material compatibility with stable interfaces, as well as tunability of the buffer layer's band gap and lattice constant by varying the atomic composition of their group-III and group-V atoms. In this study, we have achieved the molecular beam epitaxial growth of a single-crystalline CrSb $\left(\overline{1}10\right)$ thin film on a GaAs (001) substrate by inserting thin FeSb $\left(\overline{1}10\right)$ / AlAs (001) buffer layers. The in-plane epitaxial relationship is found to be CrSb [110] || GaAs [110] and CrSb [001] || GaAs $\left[1\overline{1}0\right]$, and epitaxial strain is also confirmed. We also characterized the magnetotransport properties of the grown CrSb thin film. Although the obtained conductivity tensors are mainly explained by a two-carrier model, and not by an anomalous Hall effect, this model reveals the presence of high-mobility electron and hole carriers.

Monolayer tantalum disulfide epitaxially grown on Au(111) is studied in real time during molecular beam epitaxy using low-energy electron microscopy and microdiffraction. Complementary x-ray photoelectron emission microscopy provides insight into the chemical and electronic structure of the grown layers. Our study reveals a previously unreported growth mechanism where the formation of $2\mathrm{H}\text{−}{\mathrm{TaS}}_2$ proceeds via a transient $1\mathrm{T}\text{−}{\mathrm{TaS}}_2$ phase. The $1\mathrm{T}\text{−}{\mathrm{TaS}}_2$ phase exhibits a significantly higher growth rate than the $2\mathrm{H}\text{−}{\mathrm{TaS}}_2$ phase, with growth proceeding mainly in the 1T phase. By comparison with ${\mathrm{TaSe}}_2$ on Au(111), we find that this growth mechanism is common to other Ta-based transition-metal dichalcogenides on Au(111). Furthermore, we find spectroscopic evidence for the presence of charge-density-wave order in $1\mathrm{T}\text{−}{\mathrm{TaS}}_2$ on Au(111). These findings provide perspectives on the growth dynamics and phase control of ${\mathrm{TaS}}_2$, opening up avenues for tailoring its electronic properties through substrate interaction and phase engineering.

Artificial $\text{high-}{T}_c$ superlattices (AHTS) composed of quantum building blocks with tunable superconducting critical temperature have been synthesized by engineering their nanoscale geometry using the Bianconi-Perali-Valletta (BPV) two-gap superconductivity theory. These quantum heterostructures consist of quantum wells made of superconducting, modulation-doped Mott insulators (S), confined by a metallic (N) potential barrier. The lattice geometry has been carefully engineered to induce the predicted Fano-Feshbach shape resonance between the gaps, near a topological Lifshitz transition. Here, we validate the BPV theory by providing compelling experimental evidence that AHTS samples, at the peak of the superconducting dome, exhibit resonant two-band, two-gap superconductivity. This is demonstrated by measuring the temperature dependence of the upper critical magnetic field, ${\mu }_0{H}_{\mathrm{c}2}$, in samples with superlattice periods $3.3<d<5.28$ nm and L/d ratios close to the magic value 2/3 (where L is the thickness of the superconducting ${\mathrm{La}}_2{\mathrm{CuO}}_4$ layer and $d$ is the superlattice period). The data reveal the predicted upward concavity in $H_{\mathrm{c}2}\left(T\right)$ and a characteristic kink in the coherence length as a function of temperature, confirming the predicted two-band superconductivity with Fermi velocity ratio $\approx 0.25$ and significant pair-exchange term among the two condensates.

We perform first-principles calculations on the Mo/Zr-alloyed ${\mathrm{ThMn}}_{12}$-structure prototype ${\mathrm{CeFe}}_{12}$ to explore its electronic and magnetic properties and potential for permanent magnet applications. A recent experiment has shown that the Mo/Zr-alloyed ${\mathrm{CeFe}}_{12}$ phase with the symmetry $I4/mmm$ can be stabilized in bulk. It encourages an investigation into the intrinsic magnetic characteristics of the base structure ${\mathrm{CeFe}}_{12}$ and the effect of transition metal alloying in it. Our calculations reveal that the base structure prototype ${\mathrm{CeFe}}_{12}$ in its tetragonal phase exhibits uniaxial magnetic anisotropy with a magnetic anisotropy energy ($K_1$) $\sim 1\mathrm{MJ}/{\mathrm{m}}^{-3}$ and a substantial magnetic moment of $\sim 1.8\mathrm{T}$, showing its promise as a permanent magnet. The introduction of the stabilizing transition metals Zr, Mo, and W reduces these values but still keeps the materials very promising. Notably, when 50% of Ce is substituted by Sm in Mo-alloyed ${\mathrm{CeFe}}_{12}$, the $K_1$ is significantly enhanced, accompanied by a fairly decent magnetic moment of $\sim 1.2\mathrm{T}$. These findings establish this alloy as a strong candidate for high-performance permanent magnet applications. This study emphasizes the importance of strategic element substitution and site selection in transition metal-alloyed ${\mathrm{CeFe}}_{12}$ to achieve both structural stability and remarkable magnetic properties.

We theoretically investigate the intrinsic magnon orbital Nernst effect (ONE) in noncollinear antiferromagnets with kagome spin systems. Our analysis reveals that an externally applied magnetic field induces topological phase transitions in the magnonic system, characterized by the closing and reopening of the band gap between distinct magnon bands. These transitions enable tunable control of the magnon ONE with applied magnetic field, with a pronounced enhancement in magnon orbital Nernst conductivity near the phase transition points. This tunability presents a promising direction for experimental detection of the magnon ONE.

The capabilities of additive manufacturing have facilitated the design and production of mechanical metamaterials with diverse unit cell geometries. Establishing linkages between the vast design space of unit cells and their effective mechanical properties is critical for the efficient design and performance evaluation of such metamaterials. However, physics-based simulations of metamaterial unit cells across the entire design space are computationally expensive, necessitating a materials informatics framework to efficiently capture complex structure-property relationships. In this work, principal component analysis of two-point correlation functions is performed to extract the salient features from a large dataset of randomly generated 2D metamaterials. Physics-based simulations are performed using a fast Fourier transform (FFT)-based homogenization approach to efficiently compute the homogenized effective elastic stiffness across the extensive unit cell designs. Subsequently, Gaussian process regression is used to generate reduced-order surrogates, mapping unit cell designs to their homogenized effective elastic constants. It is demonstrated that the adopted workflow enables a high-value low-dimensional representation of the voluminous stochastic metamaterial dataset, facilitating the construction of robust structure-property maps. Finally, an uncertainty-based active learning framework is utilized to train a surrogate model with a significantly smaller number of data points compared to the original full dataset. It is shown that a dataset as small as $0.61\%$ of the entire dataset is sufficient to generate accurate and robust structure-property maps.

Bottom-up synthetic approaches to synthesize stacks of individual quasi-two-dimensional materials remain a major experimental challenge. Here, we evaluate the applicability of the little-known technique of modulated elemental reactants (MER) for the synthesis of one-unit-cell-thick ${\mathrm{Bi}}_2{\mathrm{Se}}_3/{\mathrm{MoSe}}_2$ bilayer stacks via the self-assembly of amorphous elemental Bi|Se and Mo|Se precursors. Using a two-step annealing approach, both layers can be crystallized in a single heterostructure, as evidenced by a combination of x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. However, we observe a limited stability of the ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ layer, reflected in its partial decomposition under conditions required to crystallize ${\mathrm{MoSe}}_2$. The choice of substrate proves to be a crucial piece to control the thin film growth: We demonstrate the evolution of larger-scale epitaxial alignment within a heterostructure grown via MER by low-energy electron diffraction.

Due, in part, to its simultaneous transport of protons, electrons, and oxygen ions, $\mathrm{BaC}{\mathrm{o}}_{0.4}\mathrm{F}{\mathrm{e}}_{0.4}\mathrm{Z}{\mathrm{r}}_{0.1}{\mathrm{Y}}_{0.1}{\mathrm{O}}_{3–\delta }$ (BCFZY4411) is an archetypal triple-conducting oxide (TCO) and a promising candidate for the air electrode of protonic ceramic electrochemical cells. While the average nuclear structure of BCFZY4411, a cubic perovskite, is well established, several important details such as possible short-range ordering on the B site and the location of protons, features which would be expected to impact transport, are unknown. Here we apply neutron diffraction and magnetometry to probe the nuclear and magnetic structure of BCFZY4411 in both the dried state and after exposure to steam/air atmosphere. We observe a transition from short-range antiferromagnetic correlations at room temperature to uncompensated antiferromagnetic behavior with slight ferromagnetic ordering at low temperatures. The short-range magnetic correlations persist through 500 K, revealing the effects of a complex spin structure and oxidation landscape in this cubic perovskite. Rietveld refinements of neutron diffraction data show a 2–3% decrease in oxygen site vacancies, reduction in O and B site atomic displacement parameters, lattice contraction, and reduced magnetic phase-transition temperature upon exposure to steam. The hydrogen content in the steam-treated material is estimated to be below 0.15 at%, indicating that the observed changes in structure and magnetic properties are largely due to oxidation. The result indicates that a high proton concentration is not a prerequisite for high electrochemical activity. The comprehensive crystallographic analysis presented here furthermore paves the way for future quantitative studies of local atomic structure in this and other TCO systems.

Modifying molecular structure is an effective strategy to enhance the gating efficiency of an organic single-molecule field-effect transistor (FET). In this work, we investigate the gating performance of molecular devices incorporating a five-membered heterocyclic ring with two heteroatoms, $X$ and $Y$ ($X=\mathrm{NH}$, O, or S, $Y=\mathrm{N}$) positioned at 1,3-sites. Our results reveal that both the chemical identity and spatial arrangement of the heteroatoms significantly influence device performance. When the five-membered ring connects via C2 and C5 positions, the device based on an imidazole ring ($X=\mathrm{NH}, Y=\mathrm{N}$) exhibits the highest sensitivity to external gate voltage, resulting in the largest on/off current ratio. Upon alteration of the linkage to the C2 and C4 positions, equivalent to changing the relative positions of the heteroatoms, the gating efficiencies of all devices are further improved. In particular, the thiazole-based device ($X=\mathrm{S}, Y=\mathrm{N}$) demonstrates a more than eightfold increase in the on/off current ratio. An electronic structure analysis attributes this enhancement to the emergence of destructive quantum interference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, giving rise to a pronounced transmission dip. Under appropriate gate voltage, this transmission dip approaches the bias window, leading to a substantially suppressed off-state current. These findings offer theoretical insights for the design of high-performance single-molecule FETs through the targeted incorporation and positioning of heteroatoms.