We employed molecular-dynamics simulations to explore comparatively the thermomechanical behavior of two glass materials—an oxide silica glass (${\mathrm{SiO}}_2$) and a binary Cu-Zr-based metallic alloy (${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$)—during shear and elongation deformation cycles. By calculating the energy balance and tracking the temperature evolution of both glasses under deformation cycles, we are able to propose, for each of them, a constitutive law that accurately reproduces the self-heating process due to plastic deformation. These relatively simple constitutive laws involve strain rate sensitivity and a nonlinear temperature dependence of the thermal dilatancy coefficients, as well as strain gradient plasticity. To identify the right parameters, both glasses are equilibrated at very low temperature (10 K), and two independent deformation rates were applied to each sample for each type of deformation. Thermal attenuation is greatly amplified in silica compared to the metallic glass. Moreover, using a precise atomic description of the instantaneous deformation, combined with an exact coarse-graining procedure, we show, in silica, that self-heating is mainly supported by inhomogeneous strain gradient plasticity with nanometric characteristic lengthscales.

The observation of the interaction between two coupled effects of surface transfer doping (STD) and Burstein-Moss (B-M) shift on the electrical, optical, and electronic properties of ${\mathrm{V}}_2{\mathrm{O}}_5$, a layered van der Waals oxide semiconductor, is reported. Studies on bulk crystals, thin films, and powder samples show that, as a result of its high electron affinity, stoichiometric ${\mathrm{V}}_2{\mathrm{O}}_5$ exposed to humid air exhibits the phenomenon of surface transfer doping, in which a surface-absorbed water layer injects electrons into the conduction band (CB) of ${\mathrm{V}}_2{\mathrm{O}}_5$, leading to degenerate $n$-type doping, formation of a surface electron accumulation layer, and a corresponding B-M shift of the surface Fermi level of 0.25–0.6 eV well into the CB edge. In nonstoichiometric oxide (${\mathrm{V}}_2{\mathrm{O}}_{5-x}$), the presence of high density of bulk oxygen vacancy (${\mathrm{V}}_{\mathrm{O}}$) defects leads to electron doping, an increased B-M-induced $E_{\mathrm{F}}$ shift of 0.4–1.0 eV to higher energy in the bulk. In contrast, the surface $E_{\mathrm{F}}$ level remains pinned at lower energy owing to the switch in the STD effect, leading to reverse electron transfer from the oxide to the absorbed water layer, and causing the formation of an electron depletion layer on the surface. The implications of these effects for the wide variations in the reported band gap, doping, and catalysis of ${\mathrm{V}}_2{\mathrm{O}}_5$ are discussed.

Quantum magnetism based on the Kitaev honeycomb model has been intensively studied both by theoretical material design and experimental materialization. In contrast to the considerable progress of theoretical modeling and experiments on bulk crystals, it is still difficult to find a candidate material applicable to thin films and devices toward future quantum computation. Here we clearly demonstrate a Mott insulating state of $\mathrm{Ir}{\mathrm{O}}_6$ honeycomb monolayer structured in ilmenite-type $\mathrm{Mg}\text{−}\mathrm{Ir}\text{−}\mathrm{O}/\mathrm{MgTi}{\mathrm{O}}_3$ superlattices, which is a good candidate of the Kitaev honeycomb magnet applicable to devices. Electronic states detected by photoelectron spectroscopy agree well with those in theoretical band calculations. The stabilized superlattice with the Mott gap state is a promising platform to examine the device physics of the Majorana fermions and the $Z_2$ fluxes in the Kitaev honeycomb model, suggesting the thin-film techniques are quite beneficial for triggering the exploration of quantum computation in designable and evolvable heterostructures.

Gallium nitride (GaN) is a wide-bandgap semiconductor of significant interest for applications in solid-state lighting, power electronics, and radio-frequency amplifiers. An important limitation of this semiconductor is its low intrinsic hole mobility, which hinders the development of $p$-channel devices and the large-scale integration of GaN complementary metal-oxide-semiconductors in next-generation electronics. Prior research has explored the use of strain to improve the hole mobility of GaN, but a systematic analysis of all possible strain conditions and their impact on the mobility is lacking. In this study, we introduce a piezomobility tensor notation to characterize the relationship between applied strain and hole mobility in GaN. To map the strain-dependence of the hole mobility, we solve the ab initio Boltzmann transport equation, accounting for electron-phonon scattering and GW quasiparticle energy corrections. We show that there exist three optimal strain configurations, two uniaxial strains and one shear strain, that can lead to significant mobility enhancement. In particular, we predict room-temperature hole mobility of up to 164 ${\mathrm{cm}}^2/\mathrm{Vs}$ for 2% uniaxial compression and 148 ${\mathrm{cm}}^2/\mathrm{Vs}$ for 2% shear strain. Our methodology provides a general framework for investigating strain effects on the transport properties of semiconductors from first principles.

Atomic diffusion in intermetallic phases is crucial for the microstructural evolution and mechanical properties of transition-metal alloys. This study investigates diffusion in $\mathrm{L}{1}_2\text{−}{\mathrm{FeNi}}_3$ using kinetic Monte Carlo simulations with an effective interaction model parametrized on density functional theory data. By explicitly modeling atomic and spin degrees of freedom, the simulations systematically explore the effects of finite-temperature magnetochemical interplay and stoichiometry on diffusion. The results show that Fe diffuses slightly faster than Ni, contrasting the empirical rule experimentally verified in many intermetallics where the majority element diffuses faster. Non-Arrhenius behaviors of Fe and Ni diffusion are found, which are mainly attributed to the chemical rather than magnetic transitions. Activation energies for Fe and Ni atoms are predicted to be 3.22 eV in the ferromagnetic $\mathrm{L}{1}_2$ phase, approximately 0.6 eV higher than in the paramagnetic disordered phase. Magnetic excitations significantly impact diffusion properties, with notable discrepancies between the equilibrium ferromagnetic and perfectly ferromagnetic states in the $\mathrm{L}{1}_2$ phase. Deviations from stoichiometric composition lower activation energies and enhance diffusion for both Fe and Ni, which is unexpectedly similar to the trends observed in B2-type intermetallics. In the absence of experimental tracer diffusion data for the $\mathrm{L}{1}_2$ phase, this work provides reliable diffusion predictions based on a model validated in disordered Fe-Ni alloys. These results are expected to guide future studies of phase transformation and domain growth in ordered intermetallics. This work provides a detailed analysis of diffusion in $\mathrm{L}{1}_2\text{−}{\mathrm{FeNi}}_3$, contributing a broader understanding of magnetochemical and compositional effects on diffusion behavior in intermetallic alloys.

The mechanical properties of structural materials are critically affected by the solid phases that are present in their microstructure, including both their crystallographic structure and chemical order. Predicting the stability of these phases as a function of thermodynamic state variables such as temperature and composition is therefore essential for the study of mechanical properties. In equilibrium, these stabilities are determined by the free energies of the various phases, which we compute from first principles as a function of composition and temperature for the Cu-Al binary alloy. Using two types of machine-learning interatomic potentials fitted to density functional theory calculations, we perform thermodynamic integration across various paths to determine the relative free energies of liquid, face-centered cubic, body-centered cubic, and hexagonal close-packed structures, both with and without chemical ordering. We compare the resulting stable phases and phase boundaries to experimental observations in the high-temperature copper-rich region of the phase diagram. Our results demonstrate that MLIPs fitted without prior knowledge of the material's crystal structure can reproduce the first principles reference potential energy surface with sufficient accuracy and speed to bridge the length and time scales necessary for calculation of free energies, enabling phase stability calculations.

Vibrational and magnetic properties of single-crystal uranium-thorium dioxide (${\mathrm{U}}_x\mathrm{T}{\mathrm{h}}_{1-x}{\mathrm{O}}_2$) with a full range of $0<x<1$ are investigated. Thorium dioxide is a diamagnet whose thermal properties are governed by lattice vibration. The addition of paramagnetic uranium ions leads to the emergence of magnetic effects that alter the thermophysical properties noticeably even at room temperature. The interaction of phonons with magnetic moments of uranium $5f$ electrons mediated by magnetoelastic coupling results in an anomalous low-temperature thermal conductivity profile. Analysis of the magnetic susceptibility measurements indicates a departure from the Curie-Weiss relationship characteristic of noninteracting paramagnetic ions, previously associated with the dynamic Jahn-Teller (DJT) effect characterized by coupling between spin and the oxygen sublattice. The ${\mathrm{T}}_{2\mathrm{g}}$ Raman peak position follows a nonlinear trend as a function of uranium concentration and hints that these Raman active optical modes play a role in either DJT or in mediating quadrupole-quadrupole interactions. A first-principle-based thermal transport model is implemented to explain the low-temperature transport measurements, where the anomalous reduction is attributed to phonon-spin resonant scattering. The interplay between spins and phonons is also captured using high-resolution inelastic x-ray scattering (IXS) measurements of phonon linewidths. Our results provide insights into the phonon interactions with the magnetic excitations governing DJT effect and impacting the low-temperature thermal transport processes in this material system. These findings have implications for understanding low-temperature thermal transport and magnetic properties in advanced materials for information processing and energy applications.

The polycrystalline layered compounds ${\mathrm{Fe}}_{0.25}{\mathrm{TiS}}_{2-y}{\mathrm{Se}}_y$ have been synthesized using the solid-state reaction method and characterized by means of x-ray diffraction, magnetization, electrical resistivity, and magnetoresistance measurements. The iron-chalcogen bonds in ${\mathrm{Fe}}_{0.25}{\mathrm{TiS}}_{2-y}{\mathrm{Se}}_y$ are found to be noticeably longer than the titanium-chalcogen bonds, and the bond lengths increase when sulfur is replaced by selenium, although the axial ratio $c/a$ remains unchanged. Although all compounds exhibit antiferromagnetic (AFM) order below $T_N$, increasing the selenium content in ${\mathrm{Fe}}_{0.25}{\mathrm{TiS}}_{2-y}{\mathrm{Se}}_y$ changes the magnetization behavior from Ising type in selenium-poor compounds ($y<0.5$) to Heisenberg type at $y>0.5$. In compounds with mixed anionic layers, the AFM order presumably coexists with the cluster glass state. At low concentrations of selenium ($y<0.5$), the compounds exhibit irreversible field-induced phase transitions to a metastable ferromagnetic (FM) state, which are accompanied by significant remnant magnetoresistance. Reversal of magnetization in the FM state is accompanied by a large hysteresis $H_c$ (up to $\sim 50$ kOe at 2 K). In the ${\mathrm{Fe}}_{0.25}{\mathrm{TiSe}}_2$ compound ($y=2$) with Néel temperature $T_N\sim 43$ K, an anomalous electrical resistivity behavior was detected in the vicinity of 110 K, which is associated with a charge-density-wave-type transition, similar to that observed in nonintercalated ${\mathrm{TiSe}}_2$.

Fission products (FP) are inevitable byproducts of nuclear fission in the fuel during reactor operation. The migration and aggregation of FP in uranium dioxide ($\mathrm{U}{\mathrm{O}}_2$)-based nuclear fuels play a crucial role in determining fuel performance and safety throughout the nuclear fuel cycle. However, accurately characterizing the atomic diffusion and early cluster formation of FP remains challenging in experiments. To address this issue, we employed self-developed deep potential (DP) models for $\mathrm{U}{\mathrm{O}}_2$-Xe and $\mathrm{U}{\mathrm{O}}_2$-I systems to perform molecular dynamics (MD) simulations. These simulations investigate the effects of Xe and I migration and aggregation on the mechanical properties and thermal conductivity of $\mathrm{U}{\mathrm{O}}_2$ fuel. First, the accuracy of the DP models was verified. Next, the diffusion coefficients and cluster formation behavior of Xe and I in $\mathrm{U}{\mathrm{O}}_2$ were analyzed, revealing three distinct temperature-dependent diffusion mechanisms. Furthermore, the MD simulation results demonstrate that the incorporation of FP significantly reduces the mechanical properties and thermal conductivity of $\mathrm{U}{\mathrm{O}}_2$. Interestingly, the aggregation of FP into clusters mitigates these reductions, improving both mechanical properties and thermal conductivity. Notably, the recovery of mechanical properties through Xe aggregation is quite limited, primarily due to the formation of larger Xe clusters. In contrast, Xe aggregation leads to a more substantial improvement in thermal conductivity compared to I aggregation, attributed to reduced phonon scattering resulting from the fewer residual dispersed Xe atoms in the $\mathrm{U}{\mathrm{O}}_2$ matrix. These insights are critical for improving reactor safety and extending operational lifespans through a better understanding of the migration and aggregation of FP.

The recent discovery of two-dimensional electron gas (2DEG) at ${\mathrm{KTaO}}_3$-based interfacial systems has attracted considerable interest, offering great potentials for engineering novel electronic devices. Previously, influences of fabrication conditions on the 2DEG quality have been extensively studied in the thin films. However, little is known about possible influences of the device fabrication process to the 2DEG property. In this work, we have fabricated Hall bar devices with different channel widths, using the superconducting 2DEG at the amorphous-$\mathrm{LaAl}{\mathrm{O}}_3/\mathrm{KTa}{\mathrm{O}}_3$ (111) heterointerface as a prototypical system. We found that the device properties are collaboratively tuned by the channel width and the oxygen growth pressure. In particular, when the sample is grown under an intermediate oxygen pressure, an anomalous channel-width effect is observed that narrowing the channel would effectively increase the carrier density, leading to enhanced superconducting onset temperature and spin-orbit coupling. Consequently, the 2DEG properties become almost continuously tunable by adding the channel width as a new tuning parameter. Our present work contributes to exploration of explicit fabrication control of the superconducting 2DEG for novel electronic applications.

High-pressure shear band formation is a critical phenomenon in energetic materials because of its ability to form hotspots and influence mechanical strength. Shear banding is known to occur in a variety of these materials, but the governing dynamics of the mechanisms are not well defined for molecular crystals. Our previous work has found that at high pressures in 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), the initial formation sites for shear bands, called “embryos”, form in excess and rapidly lower deviatoric stresses prior to shear band formation and growth, suppressing the shear banding nucleation and growth. Here, we assess the influence of a variety of changes to the material state on this phenomenon, including altered initial temperature, lateral strain that confines the system in tension or pressure, and initial molecular vacancies throughout the crystal. Shear band suppression and the nature of the shear band network are assessed as a function of each of these.

The atomic-scale defect origins of single-photon emission in atomically thin hexagonal boron nitride (h-BN) remains an unresolved challenge, which demands precise identification to achieve its potential applications in quantum technology. High-resolution atomic force microscopy (HR-AFM) provides a noninvasive approach for obtaining an atomic-scale understanding of point defects in h-BN. Here, we examine HR-AFM imaging of a representative point defect in h-BN: a carbon substitution of boron and an adjacent nitrogen vacancy (the ${\mathrm{C}}_{\mathrm{B}}{V}_{\mathrm{N}}$ defect). We address the electronic structure of this defect using first-principles simulations based on real space pseudopotentials within density functional theory. We also resolve a common problem with estimating lateral displacement in HR-AFM simulations using conventional approaches. These approaches often overestimate the lateral displacements at small tip-sample distances. We introduce a more accurate and computationally inexpensive iterative tilt correction method. Our analysis of the spin singlet (${}^1{A}_1$) and triplet (${}^3{B}_2$) states reveals the role of out-of-plane displacements and tip heights in imaging contrast. The HR-AFM image of the ${}^1{A}_1$ state exhibits bright spot shifts with tip height due to orbital tilts, whereas the planar ${}^3{B}_2$ state shows no such shift, which further highlights the electronic orbital contribution to AFM images. We demonstrate the ability of AFM simulations to quantify the relationship of the structural geometry and electronic state configuration of point defects in two-dimensional systems.

We theoretically investigate the electronic structure of monolayer ${\mathrm{BC}}_3$ and find that it hosts anisotropic multiple valleys originating from the splitting of the van Hove singularity in graphene. To make use of its favorable electronic structure, we investigate the electronic structure of alkali-metal-intercalated ${\mathrm{BC}}_3$, where intercalated atoms not only introduce electron carriers but also suppress interlayer coupling. We find that the interlayer transfer is effectively suppressed by potassium intercalation, by which the favorable electronic structure of monolayer ${\mathrm{BC}}_3$ is preserved. Finally, we perform model calculation with the onsite-energy offset, and we verify that the strategy of introducing the splitting to the van Hove singularity works well.

We investigate the temperature dependence of the intrinsic anomalous Hall conductivity in ${\mathrm{Fe}}_3\mathrm{Ge}$, which is a ferromagnetic topological metal. We observe a significant anisotropy in the anomalous Hall conductivity between in-plane and out-of-plane directions. We further identify that the total Hall conductivity is contributed extrinsically due to the skew-scattering mechanism and intrinsically due to nonzero Berry curvature in the momentum space. Most importantly, we demonstrate the temperature dependence of the intrinsic Hall contribution, a rare phenomenon to visualize experimentally, due to tuning the easy-magnetic axis from the out-of-plane to the in-plane with decreasing temperature. We also show that the extrinsic Hall conductivity decreases with temperature as ${\sigma }_{xy}^{\mathrm{ext}}\left(T\right)=\frac{{\sigma }_{xy0}^{\mathrm{ext}}}{{(aT+1)}^2}$ due to electron-phonon scattering.

We study experimentally the impact of the additive fabrication method on the magnetic properties of ${\mathrm{Fe}}^{+}$-implanted Pd square artificial spin ice lattices. Our findings show that the lattices exhibit a higher ordering temperature than their continuous film counterparts. This behavior is attributed to the additive fabrication process, which induces an inhomogeneous Fe concentration within the lattice building blocks. Moreover, the implantation process creates a magnetic depth profile, enabling temperature-dependent tunability of the magnetic thickness. These additional internal degrees of freedom broaden the design possibilities for magnetic metamaterials, allowing precise fine tuning of their static and dynamic properties to achieve complex and customizable behaviors.

The high specific capacity of Li-ion batteries requires a high Li ratio anode. However, a high Li ratio indicates the structure of the anode compound is complicated. For compounds with similar elements, a more complicated crystal structure usually means a lower thermal transport property based on the classical Slack model, i.e., the thermal conductivity of crystals is negatively correlated with the number of atoms in primitive cells, which inevitably increases the risk of thermal runaway and seriously hinders the widespread use of Li-ion batteries. In this study, however, our machine-learning-potential-based atomistic simulations show that the room temperature thermal transport capacity of a possible complicated anode candidate $\mathrm{L}{\mathrm{i}}_{15}\mathrm{S}{\mathrm{i}}_4$ (i.e., $\sim 3.0$ W/m/K and a theoretical capacity of 1857.26 mAh/g) is comparable to that of the traditional anode LiSi (i.e., $\sim 3.28$ W/m/K and a theoretical capacity of 765.1 mAh/g). Our spectral analysis shows that the increase of the Li ratio will generate many optical branches with frequencies higher than 4 THz and largely decrease the specific heat of vibrations below 4 THz. Meanwhile, these vibrations with frequencies lower than (above) 4 THz are found to mainly transfer thermal energy through propagating (both propagating and coherence) channels. The thermal conductivity contributed from vibrations with frequencies lower than 4 THz decreases from 2.54 W/mK for LiSi to1.99 W/mK for $\mathrm{L}{\mathrm{i}}_{15}\mathrm{S}{\mathrm{i}}_4$. However, the smaller frequency difference among vibrations with frequencies above 4 THz in $\mathrm{L}{\mathrm{i}}_{15}\mathrm{S}{\mathrm{i}}_4$ are found to increase the thermal transport capacities of these vibrations via the overwhelming coherence channel compared to the propagating channel. The thermal conductivity contributed from these vibrations is 1.01 W/mK for $\mathrm{L}{\mathrm{i}}_{15}\mathrm{S}{\mathrm{i}}_4$ and 0.74 W/mK for LiSi. As a result, $\mathrm{L}{\mathrm{i}}_{15}\mathrm{S}{\mathrm{i}}_4$ with a complicated crystal structure possesses a similar thermal transport capacity compared to the simple crystal LiSi.