We propose a computational scheme for the diffusion and retention of multiple hydrogen isotopes (HI) with multi-occupancy traps parametrized by first principles calculations. We show that it is often acceptable to reduce the complexity of the coupled differential equations for gas evolution by taking the dynamic steady state, a generalization of the Oriani equilibrium for multiple isotopes and multi-occupancy traps. The effective gas diffusivity varies most with mobile fraction when the total gas concentration approximates the trap density. We show HI binding to a monovacancy in vanadium produces a nonmonotonic dependence between diffusivity and gas concentration, unlike the tungsten system. We demonstrate the difference between multiple single occupancy traps and multi-occupancy traps in long-term diffusion dynamics. The applicability of the multi-occupancy, multi-isotope model in steady state is assessed by comparison to an isotope exchange experiment between hydrogen and deuterium in self-ion irradiated tungsten. The vacancy distribution is estimated with molecular dynamics, and the retention across sample depth shows good agreement with experiment using no fitting parameters.

The orthorhombic $\mathrm{LiGa}{\mathrm{S}}_2$ is widely used in nonlinear optical devices due to its wide direct optical band gap (4.15 eV). Nonetheless, its large hole effective mass results in low hole mobility, which severely limits its applications as p-type semiconductor. In this work, the tailored alloying strategy and valence band engineering scheme are adopted to raise the valence band maximum and decrease the hole effective mass. Based on the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional calculations, the structural, electronic, and optical properties and stability for $\mathrm{L}{\mathrm{i}}_{1-x}\mathrm{C}{\mathrm{u}}_x\mathrm{Ga}{\mathrm{S}}_2$ alloys are predicted. The unfolded band structure reveals that Cu alloying primarily modifies the valence bands. Higher Cu-$3d$ orbitals can elevate the valence band maximum of the alloys. The enhanced $p\text{−}d$ hybridization in the valence bands significantly reduces the hole effective mass. Specifically, along the Γ-Y direction, the hole effective mass for $\mathrm{L}{\mathrm{i}}_{0.625}\mathrm{C}{\mathrm{u}}_{0.375}\mathrm{Ga}{\mathrm{S}}_2$ alloy is reduced from $1.95m_0$ to $0.494m_0$, where $m_0$ is the free electron mass, representing a 75% reduction. Moreover, the excellent visible light transparency for $\mathrm{L}{\mathrm{i}}_{0.625}\mathrm{C}{\mathrm{u}}_{0.375}\mathrm{Ga}{\mathrm{S}}_2$ alloy is preserved. These findings provide an important insight into the design of optoelectronic devices based on $\mathrm{L}{\mathrm{i}}_{0.625}\mathrm{C}{\mathrm{u}}_{0.375}\mathrm{Ga}{\mathrm{S}}_2$ alloy.

Because of the challenges associated with the fabrication of aligned CNT-based bulk composites, a two-frequency electric-field-assisted method is proposed herein to prepare composites enhanced with bundle-structured CNTs (b-CNTs), which is markedly different from the results of a random arrangement or conventional alignment using a fixed-frequency electric field. As-prepared b-CNTs notably improve the mechanical and electrical properties of polyurethane acrylate (PUA), achieving a 57.2% higher flexibility and a 68.2% larger dielectric constant than pure PUA. The effects of the electric field frequencies on the arrangement of CNTs are investigated to understand the dynamic processes associated with aligning CNTs in the polymer solution, which are mainly governed by the interplay between dielectrophoretic forces and fluid-induced shear stress on CNTs. Such a solution-based method can be adapted to efficiently fabricate large-size functional composites.

Transition metal dichalcogenides (TMDs) represent an emerging class of layered materials with applications in microelectronics, optoelectronics, photonics, and catalysis. The confinement of charge carriers within the highly anisotropic, quasi-two-dimensional geometry of one-layer (1L) TMDs leads to reduced, variable dielectric screening, giving rise to a quasiparticle band gap that is highly susceptible to the surrounding dielectric environment. Exploiting the contrasting external dielectric environments of gold-supported and suspended 1L $\mathrm{W}{\mathrm{S}}_2$, we show how the electronic states of $\mathrm{W}{\mathrm{S}}_2$ under the effective and ineffective screening environments align at a junction made within the same sheet of material. Photoelectron spectra point to the close alignment of the charge neutrality levels of $\mathrm{W}{\mathrm{S}}_2$ in both environments, and the breakdown of rigid shifts between the valence states and core levels with the core levels shifting more than twice as much as the valence states. Furthermore, the effectively screened $\mathrm{W}{\mathrm{S}}_2$ exhibits a valence state with the photoemission linewidth twice as large as the ineffectively screened suspended $\mathrm{W}{\mathrm{S}}_2$, presumably originated from the locally varying $\mathrm{W}{\mathrm{S}}_2$-Au distance and substrate disorders. Collectively, these findings provide key insights into the electronic behavior of $\mathrm{W}{\mathrm{S}}_2$ and its photoemission process with the electronic states renormalized according to the external screening environments.

Bi alloying is predicted to transform GaAs from a semiconductor to a topological insulator or semimetal. To date, studies of the ${\mathrm{GaAs}}_{1-x}{\mathrm{Bi}}_x$ alloy band structure have been limited, and the origins of Bi-induced enhancement of the spin-orbit splitting energy, ${\mathrm{\Delta }}_{\mathrm{SO}}$, are unresolved. Here, we present high-resolution angle-resolved photoemission spectroscopy of droplet-free epitaxial ${\mathrm{GaAs}}_{1-x}{\mathrm{Bi}}_x$ films with $x_{\mathrm{Bi}}=0.06$. In addition to quantifying the Bi-induced shifts of the light-hole and heavy-hole valence bands, we probe the origins of the Bi-enhanced ${\mathrm{\Delta }}_{\mathrm{SO}}$. Using exact-two-component density functional theory calculations, we identify the key role of Bi $p$-orbitals in the upward shift of the light-hole and heavy-hole bands that results in the Bi-enhanced ${\mathrm{\Delta }}_{\mathrm{SO}}$.

We report on the high-pressure optical and mechanical properties of penta-twinned gold nanoparticles (PT-AuNPs) of different geometries: decahedra, rods, and bipyramids. Our results show that, unlike single-crystal gold nanoparticles (SC-AuNPs), PT-AuNPs preserve both their noncubic crystal structures and their overall morphology up to 30 GPa. This structural integrity under compression is related to an enhanced mechanical resilience of PT-AuNPs, despite exhibiting bulk moduli comparable to those of SC-AuNPs. Notwithstanding, comparable pressure-induced localized surface plasmon resonance redshifts—for all nanoparticle geometries—were observed. Our analysis indicates that these shifts are primarily caused by changes in the refractive index of the surrounding medium, with electron density compression playing a minor role, contrasting with the behavior in SC-AuNPs, where electron density compression has a greater influence.

Ferroelectricity can emerge in vertically stacked two-dimensional materials even when their constituent monolayers are nonferroelectric. In these sliding ferroelectrics, polarization switching is driven by small lateral displacements between layers. Here, we develop a comprehensive materials design framework for slidetronics founded on a symmetry principle: any sliding-induced polarization change from a state $\mathit{P}$ to ${\mathit{P}}^{\prime }$ can be equivalently described by applying an appropriate point-group operator, or “generator” $G$, to the entire system, such that ${\mathit{P}}^{\prime }=G\mathit{P}$. This generator-based framework classifies all possible sliding-induced transformations, establishes the necessary symmetry conditions for switchable polarization components, and provides design strategies for realizing targeted switching behaviors. A central result is that complete polarization inversion is symmetry forbidden in bilayers but becomes possible in multilayers. First-principles calculations confirm these predictions, revealing novel phenomena including dipole-locked ferroelectricity in cellulose bilayers, in-plane switching in ${\mathrm{As}}_2{\mathrm{S}}_3$-based systems, and full polarization reversal in a ${\mathrm{PdSe}}_2$ trilayer.

High-entropy metal nitrides are an important material class in a variety of applications, and the role of nitrogen vacancies is of great importance for understanding their stability and mechanical properties. We study six different high-entropy nitrides with eight different metal species to build a predictive model of the nitrogen-vacancy formation energy. We construct sets of supercells that maximize the number of unique nitrogen environments for a given chemistry, and then use density-functional theory to calculate the energy density for all nitrogen sites, and the vacancy formation energies for the highest, lowest, and a median subset based on the energy densities. The energy density of nitrogen sites correlates with the vacancy formation energies, for binary, ternary, and high-entropy nitrides. A linear regression model predicts the vacancy formation energies using only the nearest-neighbor composition; across our eight metals, we find the largest vacancy formation energies next to Hf, then Zr, Ti, V, Cr, Ta, Nb, and the lowest near Mo. Additionally, we see that binary nitride data show qualitatively similar vacancy formation energy trends for high-entropy nitrides; however, the binary data alone are insufficient to predict the complex nitride behavior. Our model is both predictive and easily interpretable, and correlates with experimental data.

We report an ab initio study of phase stability, defect formation, electronic structure, and multiple magnetic, Dzyaloshinskii-Moriya, optical, hyperfine, and crystal field interactions in erbium (Er)-doped wide band gap $\alpha$- and $\beta$-gallium oxides (${\mathrm{Ga}}_2{\mathrm{O}}_3$), critically important to make a foundation for both optoelectronic and quantum information applications. The chemical, structural, mechanical, and dynamical stabilities of the pristine phases are confirmed from respective negative formation energies, negative cohesive energies, favorable elastic constants, and positive phonon frequencies. The phonon dispersions indicate that the Ga-O bonds are uniform in the $\alpha$-phase, while they vary in the $\beta$-phase due to the anisotropic polyhedral movement. The defect formation energy analysis confirms that both Er-doped $\alpha$- and $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ prefer ${\mathrm{Er}}^{3+}$ (neutral) state. The underestimated band gaps of the pristine phases from standard density functional theory (DFT) calculations as compared to experimental values are corrected by employing the hybrid functional calculations, resulting in the indirect band gaps of 5.21 eV in $\alpha \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ and 4.94 eV in $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ . The site preference energy analysis indicates partial occupation of Er in the octahedral site of Ga. The anisotropic nature of hyperfine tensor coefficients of Er is similar in both phases, which may be due to the occupation of Er in the same octahedral Ga site. On the other hand, the calculated magnetic exchange interaction between two Er dopants is negative for $\alpha$ and positive for $\beta$, indicating an antiferromagnetic (AFM) ground state in the former and a ferromagnetic (FM) ground state in the latter. Large values of Dzyaloshinskii-Moriya interactions (DMIs) are obtained along the $x$ direction in the $\alpha$ and along the $y$ direction in the $\beta$. The large DMI may support exotic magnetic textures, a promising direction for spintronic applications. The analysis of dielectric constants and refractive indices of both pristine and Er-doped phases shows a good agreement with available experimental values. The calculated optical anisotropy is slightly higher in $\beta$ than those in $\alpha$, which is due to the involvement of lower symmetry in $\beta$. The crystal field coefficients (CFCs) calculated from DFT are used to analyze $4f$ multiplets and $4f-4f$ transitions. Thus calculated lowest energy level of the first excited state to the lowest energy level of the ground state is about 1.53 $\mu \mathrm{m}$, which is in a good agreement with available experiments, and it falls within the quantum telecommunication wavelength range.

Precise control of defects in two-dimensional materials is crucial for their application in functional devices. Raman spectroscopy is a key technique for identifying the number of layers and strain in ${\mathrm{MoS}}_2$. Changes in the peak area ratio of the Raman active modes $A_{1\mathrm{g}}$ and $E_{2g}^1$ measured on monolayer (ML) ${\mathrm{MoS}}_2$ have, so far, only been correlated to changes in the excitation wavelength of the laser, i.e., resonant effects. However, the role of sulfur vacancies ($V_{\mathrm{S}}$) on this peak area ratio is not well studied. In this study, we show on ALD-grown ${\mathrm{MoS}}_2$ that changes in the peak area ratio of the $A_{1\mathrm{g}}$ and $E_{2\mathrm{g}}^1$ Raman modes depend sensibly on the number of $V_{\mathrm{S}}$ in the film. Raman measurements carried out with three different excitation wavelengths are combined with detailed x-ray photoelectron spectroscopy measurements to quantify the number of $V_{\mathrm{S}}$ in the film and to study their impact on vibrational properties. $V_{\mathrm{S}}$-poor ${\mathrm{MoS}}_2$ displays a stronger $A_{1\mathrm{g}}$ mode compared to the $E_{2\mathrm{g}}^1$ mode, whereas the ratio is reversed in $V_{\mathrm{S}}$-rich films. We propose that this effect originates from modifications in the electronic band structure of ML ${\mathrm{MoS}}_2$. Based on this experimental work, we propose that the peak area ratio of the $A_{1\mathrm{g}}$ and $E_{2\mathrm{g}}^1$ modes could be used as a fingerprint for the qualitative evaluation of the S deficiency in ${\mathrm{MoS}}_2$ MLs, which could be an easy-to-apply method for the quality assessment in industrial applications.

The realization of long-range spin order in two dimensions (2D) has catapulted the search for layered materials with magnetic ordering above room temperature. These efforts aim to understand and enhance the spin–spin interactions in 2D. An emergent class of such magnets is the layered ${\mathrm{Fe}}_N{\mathrm{GeTe}}_2$ (N $=3$, 4, and 5). Here, we investigate the magnetic states over a wide field–temperature phase space in the high-$T_{\mathrm{c}}$ ferromagnet ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ using magnetization, ferromagnetic resonance (FMR), and magnetotransport measurements. Our findings reveal a magnetic phase transition from a collinear to a complex noncollinear magnetic order near the temperature $T^{*}\approx 160$ K, below which magnetic susceptibility is reduced, FMR linewidth broadened, and anomalous Hall resistivity suppressed. Such noncollinearity results from the competition between magnetocrystalline anisotropy and Dzyaloshinskii–Moriya interaction arising from the unusual Fe1 ordering in two possible split sites. Our study focuses on the strategy to quench the noncollinear spin order. Substituting 40% Ni in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ is found to be one such quenching strategy. This provides deeper insights into the magnetism of a high-$T_{\mathrm{c}}$ layered ferromagnet, offering opportunities to develop 2D magnet-based devices.

We present a first-principles investigation of the excitonic properties of magnesia (MgO), an ionic insulator known to host hole polarons. We combine a density functional theory-based approach for structural relaxation in the presence of the hole and many-body perturbation theory to describe the excitonic properties. We determine that the hole polaron introduces new in-gap occupied states 0.6–0.8 eV above the valence band maximum that lead to two low-energy peaks in the optical spectrum. The predicted redshift of the lowest-energy transition due to polaron formation of 0.8 eV agrees well with the experimental Stokes shift of 0.8–0.9 eV. Analysis of the exciton wave function indicates that the electron-hole pair consists of a localized hole and delocalized electron, but that the wave function retains its Wannier-Mott character even in the presence of the hole polaron. Our study demonstrates that combining these previously established methods allows for a relatively computationally inexpensive approach to studying the exciton polaron in materials where only one charge carrier forms a polaron.

Bismuth exhibits a Peierls distortion away from a simple cubic structure, reflecting both an anharmonic potential energy surface and electron-phonon coupling in a semimetal. It has attracted considerable interest in studies of low-temperature thermal transport, thermoelectrics, and optical excitation of coherent phonon. Yet, the temperature-dependence of phonons in bismuth has remained relatively unexplored. We report extensive inelastic neutron scattering (INS) and first-principles simulations of the lattice dynamics in bismuth, including phonon energy shifts and linewidths as a function of temperature. Comprehensive four-dimensional data across the momentum ($\mathbf{Q}$) - energy ($E$) space were collected at temperatures from 2 to 300 K. Moreover, the intrinsic linewidth of TA modes was resolved using inelastic neutron spin echo with a Wollaston prism apparatus, surpassing the limitations of conventional neutron spectrometry techniques. Our results quantify the softening of phonon frequencies and suppression of phonon lifetimes at elevated temperatures, with experiments and simulations showing excellent agreement. Further, we analyzed the scattering phase space through simulations, assessing the scattering channels between acoustic and optic phonon modes that dominate the thermalization of photo-excited coherent optic phonons. These findings enhance our understanding of phonon-phonon interactions in bismuth and provide insights into the influence of lattice anharmonicity on its thermal properties.

Modulating magnetic anisotropy energy (MAE) by an electric field provides a powerful approach for advancing multiferroic materials and spintronic applications. In this work, we utilize first-principles calculations to investigate the electric field control of MAE in two-dimensional multiferroic materials ${\mathrm{CuCrP}}_2{\mathrm{S}}_6$ and ${\mathrm{CuMoP}}_2{\mathrm{S}}_6$, which belong to transition-metal thiophosphates (MTPs). Our results show a quasilinear relationship between MAE and the electric field, with the sign of induced changes in MAE varying based on the field's direction. This change in MAE is driven by two distinct and independent effects in the monolayer's response to the electric field: electronic and field-induced structural effects. Both effects on the MAE are enabled by the monolayer's asymmetry due to its ferroelectric nature. The electronic effect arises from the energy shifts of the $p$ states of the inequivalent (top and bottom) sulfur layers, which impact the density of states of the valence-band-edge majority-spin $d_{z^2}$ orbitals of the magnetic central atom, thereby modifying the MAE. The structural effect on the MAE is primarily attributed to the effect of an inverse-piezoelectric strain, which is manifested as a variation in the monolayer thickness. The trend of this induced strain is controlled by the difference in effective charges between the top and bottom sulfur layers. These findings offer insights into the tunability of MAE via electric fields, and they highlight potential MTP candidates for switching of MAE.

We report on the structural characterization and physical properties of ${\mathrm{Eu}}_2{\mathrm{InTe}}_5$, a distorted square-net motif antiferromagnetic semiconductor. Single crystal x-ray diffraction measurements reveal a distortion of the Te square-net layers such that an orthorhombic supercell is necessary to accurately describe the structure. Magnetization, resistivity, and specific heat measurements confirm antiferromagnetic ordering at $T_N=7.3\mathrm{K}$. Anisotropy in magnetization data suggests the magnetic moments are oriented parallel to the $c$ axis. We observe an unconventional transverse magnetoresistance and Hall resistivity in the paramagnetic state ($T\le 80\mathrm{K}$), indicating strong coupling between localized ${\mathrm{Eu}}^{2+}$ magnetic moments and conduction electrons. Resistivity and Hall measurements indicate the material is a heavily doped semiconductor, with impurity states related to disorder. Our findings highlight a relatively unexplored Eu-based antiferromagnetic semiconductor with unconventional magnetotransport behavior.

Parity-time-reversal-symmetric odd-parity antiferromagnetic (AFM1) materials are of interest for their symmetry-enabled quantum transport and optical effects. These materials host odd-parity terms in their band dispersion, leading to asymmetric energy bands and enabling responses such as the magnetopiezoelectric effect, nonreciprocal conductivity, and photocurrent generation. In addition, they may support a nonlinear spin Hall effect without spin-orbit coupling, offering an efficient route to spin current generation. To identify such materials, we first applied a graph neural network model with AFM1-specific symmetry constraints to screen Materials Project compounds for high-probability candidates. We then performed density functional theory calculations to compare magnetic configurations and confirmed 15 materials where AFM1 is the most stable state. The identified set comprises three experimentally verified AFM1 materials, six synthesized compounds with unknown magnetic structures, and six that are not yet synthesized.

Ultrastable glasses can be produced via vapor deposition, exhibiting superior thermodynamic and kinetic stability compared to their liquid-cooled counterparts. Although often considered equivalent to liquid-cooled glasses aged for ${10}^6$ of years, their structural evolution with increasing stability remains poorly understood. Here, using Cs-corrected scanning transmission electron microscopy, we directly observe the nanoscale spatial heterogeneity of vapor-deposited and liquid-cooled Zr-Cu-Al metallic glasses as a function of stability or energy. We find that the correlation length of spatial heterogeneity reaches a minimum in the most stable vapor-deposited metallic glasses with lowest energy, whereas larger heterogeneity is observed in the more stable liquid-cooled glasses. Complementary simulations reveal that this minimization of heterogeneity arises from the reduction of distorted icosahedral structures with medium-range ordering. Our study provides compelling evidence that vapor-deposited metallic glasses undergo a distinct evolution of spatial heterogeneity compared to their liquid-cooled counterparts as stability increases.