The charge density wave (CDW) state is a widespread phenomenon in low-dimensional metals/semimetals. The spectral weight of the associated folded bands (shadow bands) can be an intriguing trigger leading to additional Fermi surface instability and unexplored phase transitions. The rare earth tri-telluride ${\mathrm{CeTe}}_3$ exhibits a single CDW stabilized below $\sim 400\mathrm{K}$ and antiferromagnetism below $\sim 3\mathrm{K}$. The distinct periodicities between the Te-square net, the CeTe block layer, and the CDW give rise to rich shadow band formations. In this work, we reveal the predominant scattering between the original and shadow bands at 4 K, with the scattering within the original bands being relatively suppressed at Fermi energy. This unconventional quasiparticle scattering collectively underscores the vital role of the shadow bands' spectral weight and the exotic hidden matrix element effect, which are crucial for controlling electronic properties in this system. Furthermore, our finding points to the existence of rich and unexplored Fermi surface instabilities, which potentially play a role in controlling the nature of long-range antiferromagnetism at lower temperatures in the presence of finite charge-spin interaction.

Accurately predicting carrier mobility in strongly anharmonic solids necessitates a precise characterization of lattice dynamics as a function of temperature. We achieve consistency with experimental electron mobility data for bulk ${\mathrm{KTaO}}_3$ and ${\mathrm{SrTiO}}_3$ above 150 K by refining the Boltzmann transport equations. This refinement includes incorporating temperature-dependent anharmonic phonon eigenfrequencies and eigenmodes into the electron-phonon interaction tensor, while maintaining the derivatives of the Kohn-Sham potential as computed in density functional perturbation theory. Using efficient machine-learned force fields and the stochastic self-consistent harmonic approximation, we accurately compute the dynamical matrices. At room temperature, the calculated mobility for ${\mathrm{SrTiO}}_3$ exceeds experimental values by an order of magnitude, whereas the overestimation for ${\mathrm{KTaO}}_3$ is much less pronounced. This discrepancy is explained through the more significant electron mass renormalization near the conduction-band bottom due to anharmonic electron-phonon coupling and the presence of local disorder in ${\mathrm{SrTiO}}_3$.

To enhance the protection of Ni-based superalloys in gas turbine engines’ high-temperature environments, it is crucial to develop advanced thermal/environmental barrier coating (T/EBC) materials with a balanced combination of thermal, environmental, and mechanical properties. This optimization is essential to safeguard against chemical and thermal challenges at high temperatures. In this study, we harness the power of density functional theory (DFT) in conjunction with combinatorial chemistry methodologies to engineer high-performance, high-entropy rare earth aluminum garnets of the $\mathit{R}{}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ family (where $R$ denotes Y, Gd, Er, and Yb). These materials are meticulously designed to exhibit superior phase stability, a targeted coefficient of thermal expansion (CTE), low lattice thermal conductivity, and robust mechanical properties. The determination of CTE values is accomplished through phonon calculations at various volume settings within the quasiharmonic approximation, while lattice thermal conductivities are rigorously assessed employing the Debye-Callaway model, accounting for three distinct phonon processes. Our findings highlight the remarkable attributes of the solid solution ${\left({\mathrm{Y}}_{1/4}{\mathrm{Gd}}_{1/4}{\mathrm{Er}}_{1/4}{\mathrm{Yb}}_{1/4}\right)}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$, which displays a noticeable reduction in lattice thermal conductivity compared to its individual constituents while maintaining a favorable range of CTE values. The T/EBC materials, distinguished by their multifaceted functionalities, are promising next-generation T/EBCs for protecting nickel-based superalloys in gas turbine engines. Furthermore, this work serves as a testament to the efficacy and reliability of our computational framework, which holds the potential to expedite the design of next-generation T/EBC materials.

Magnetically induced ferroelectrics in multiferroics provide an optimal approach to the pursuit of intrinsically strong magnetoelectricity. However, the complex antiferromagnetism, faint magnetically induced polarization, and low working temperatures make their magnetoelectric performance incompetent from the application's demands. Here, a family of two-dimensional $5d$ halides $\mathrm{Os}{X}_2$ monolayers is predicted to be ferroelectric and ferromagnetic above room temperature. More interestingly, benefiting from the strong spin-orbital coupling and high-spin state of ${\mathrm{Os}}^{2+}$ ion, the magnetically induced ferroelectric polarization can reach $5.9\mu \mathrm{C}/{\mathrm{cm}}^2$, a record-large value in type-II multiferroics. The magnetoelectric effect, that is, controlling ferroelectric polarization by magnetic field has been demonstrated, and magnetically driven ferrovalley also emerges in this system. This work provides an effective way to solve the main defects of type-II multiferroics.

Cubic boron nitride (c-BN) is an ultrawide-bandgap semiconductor of significant interest for high-frequency and high-power electronics applications owing to its high saturation drift velocity and high electric breakdown field. Beyond transistors, devices exploiting the valley degree of freedom or negative differential resistance are of keen interest. While diamond has been found to have potential for these applications, c-BN has not been considered owing to a lack of knowledge of the relevant charge transport properties. Here, we report a study of the high-field transport and noise properties of c-BN using first-principles calculations. We find that c-BN exhibits an abrupt region of negative differential resistance (NDR) below 140 K, despite the lack of multivalley band structure typically associated with NDR. This feature is found to arise from a strong energy dependence of the scattering rates associated with optical phonon emission. The high optical phonon energy also leads to an intervalley scattering time rivaling that of diamond. The negative differential resistance and long intervalley scattering time indicate the potential of c-BN for transferred-electron and valleytronic devices, respectively.

The impact of defect generation during irradiation on grain boundary (GB) properties and associated transport phenomena lacks fundamental understanding, despite the influence GBs are known to exert over properties such as swelling, sintering, and creep. In this study, a cluster dynamics model is developed that predicts steady-state concentrations of defects at ${\mathrm{UO}}_2$ GBs by tracking the rate of point defect production and depletion, under irradiation conditions. Fast U interstitial self-diffusivity in bulk ${\mathrm{UO}}_2$ under irradiation results in their flux to GBs exceeding that of slower U vacancies. Incorporation of these interstitials at fission gas bubbles located at the GB results in their over-pressurization and cessation as effective sinks. As a consequence, U interstitials are predicted to be significantly enhanced in concentration under irradiation at ${\mathrm{UO}}_2$ GBs, and their fast mobility relative to defects in the bulk results in GB U self-diffusion orders of magnitude greater than that in the bulk. Creep controlled by diffusion of defects at GBs—Coble creep—is calculated using the predicted enhanced U self-diffusivity. The modeled creep rates compare favorably with experimental irradiation creep measurements, exhibiting the correct athermal behavior when GB defects are within a sink-limited regime. ${\mathrm{UO}}_2$ was studied here—the standard nuclear fuel—however, we expect the physical processes governing our results to extend beyond ${\mathrm{UO}}_2$.

Refractory multiprincipal element alloys (RMPEAs), a relatively new class of alloys, are attractive not only for ultrahigh strengths but also for low rates of decay in strength with temperature relative to those of any of its constituent elements. The thermally activated glide of screw dislocations is known to be responsible for the strength reduction with temperature seen in the constituents, but whether the same is true in the RMPEAs has yet to be clarified. Here, we use a three-dimensional phase-field dislocation dynamics approach combined with Langevin dynamics to investigate the thermally activated glide of long screw dislocations in the equiatomic RMPEA MoNbTaVW. In the low homologous temperature range of $0.01{\mathrm{T}}_{\mathrm{m}}-0.3{\mathrm{T}}_{\mathrm{m}}$ (900 K), we determine the temperature-dependent threshold stress at which screw glide transitions from jerky to smooth for MoNbTaVW and one of its constituents Nb. Consistent with experimental yield strengths, this critical strength decays slowly but continuously over the entire temperature range for the RMPEA, whereas it decays quickly and then plateaus at $0.16{\mathrm{T}}_{\mathrm{m}}$ for Nb. We also show that the glide mechanisms in the RMPEA and Nb transition twice with each change accompanied by a change in glide line morphology and mobility. Unlike in the RMPEA, in Nb, the second change causes the strength to stabilize with temperature. In a postmortem simulation, wherein the loaded system is subsequently unloaded and returned to 300 K, the wavy line morphologies, characteristic of the glide mechanism, are retained in RMPEAs, but the dislocation nearly recovers its original screw configuration in Nb.

Ternary SiGeSn alloys have emerged as a promising material system for applications in diverse fields such as photonics, electronics, and thermoelectrics. Its development still requires understanding the alloy properties, where an important role is alleged to be the local arrangement of the Si, Ge, and Sn atoms. Structural properties of SiGeSn epitaxial layers deposited on Ge/Si virtual substrates are investigated here by polarized Raman spectroscopy; in particular, we selected a series of samples with Ge content of $\sim 83$ at.% and variable Si and Sn content. This technique, which provides access not only to the energy but also to the symmetry of the vibrational modes, makes it possible to observe the effect of composition on the local alloy ordering. By studying how the Raman modes change the energy and the relative intensity variation under different polarization configurations, we could isolate the role of alloy configuration as the composition varies. High Sn content appears to promote local ordering, as Sn atoms tend to repel other Sn and Si atoms. Our results are potentially of great interest in elucidating SiGeSn material properties that are still debated in the literature, e.g., the influence of composition on the bandgap directness of the alloy.

 A phase field model is used to investigate how the corrosion rate and morphology of a dealloying metal is controlled by the kinetic rates of bulk solid diffusion, interfacial diffusivity, and interface dissolution. A specific focus is investigating the manner by which variations in these kinetic parameters synergistically influence the onset of a morphological instability at the solid-liquid interface, which is known to precede rapid dealloying corrosion towards highly topologically complex structures such as bicontinuous porous solids. This work demonstrates that this instability can be suppressed by either an increase of interdiffusion in the solid alloy, or by a decreasing rate of dissolution at the solid-liquid interface. When the instability is suppressed, the result is a relatively planar, passivated dealloying front. Importantly, however, coupled changes in kinetic parameters can also promote the morphological instability and sustain fine-scale ligament and pore formation. Finally, the relevance of the solid-liquid interfacial diffusion for determining the rate of dealloying and ligament formation is highlighted. By elucidating the mechanistic influence of bulk and interfacial kinetic factors on the dealloyed morphology, this work helps to rationalize the contrasting morphologies observed in various dealloying systems.

Local chemical environments of multicomponent crystals are parametrized according to basis vectors of their irreducible invariant subspaces. These short-range order parameters enable Taylor expansions of configurational properties that easily incorporate additional couplings. As one example, expansions including long-range composition can describe the energies of many alloys more accurately than conventional cluster expansions while using far fewer neighbors and basis functions.

The large amount of powder diffraction data for which the corresponding crystal structures have not yet been identified suggests the existence of numerous undiscovered, physically relevant crystal structure prototypes. In this paper, we present a scheme to resolve powder diffraction data into crystal structures with precise atomic coordinates by screening the space of all possible atomic arrangements, i.e., structural prototypes, including those not previously observed, using a pre-trained machine learning (ML) model. This involves (i) enumerating all possible symmetry-confined ways in which a given composition can be accommodated in a given space group, (ii) ranking the element-assigned prototype representations using energies predicted using the Wyckoff representation regression  ML model [Goodall et al., Sci. Adv. 8, eabn4117 (2022)], (iii) assigning and perturbing atoms along the degree of freedom allowed by the Wyckoff positions to match the experimental diffraction data, and (iv) validating the thermodynamic stability of the material using density-functional theory. An advantage of the presented method is that it does not rely on a database of previously observed prototypes and is, therefore capable of finding crystal structures with entirely new symmetric arrangements of atoms. We demonstrate the workflow on unidentified x-ray diffraction spectra from the ICDD database and identify a number of stable structures, where a majority turns out to be derivable from known prototypes. However, at least two are found not to be part of our prior structural data sets.

We investigate the growth of two-dimensional (2D) crystals on fluctuating surfaces using a phase-field crystal model that is relevant on atomic length and diffusive time scales. Motivated by recent experiments, which achieved unprecedented fast growth of large-size high-quality 2D crystals on liquid substrates, we uncover novel effects of liquid surfaces on microstructural ordering. We find that substrate fluctuations generate short-ranged noise that speeds up crystallization and grain growth of the overlayer, surpassing that of free-standing system. Coupling to the liquid substrate fluctuations can also modulate local randomness, leading to intriguing disordered structures with hidden spatial order, i.e., disordered hyperuniformity. These results reveal the physical mechanisms underlying the fast growth of 2D crystals on liquid surfaces, and demonstrate a novel strategy for synthesizing disordered hyperuniform thin film structures.

In this study, the influence of $5|7$ dislocations in multilayer graphene stacks (up to six layers) is examined. The study is conducted using a recently developed phase-field crystal (PFC) model for multilayer systems incorporating out-of-plane deformations and parameterized to match to density functional theory calculations for graphene bilayers and other systems. The specific configuration considered consists of one monolayer containing four $5|7$ dislocations (i.e., two dislocation dipoles) sandwiched between perfect graphene layers. This study reveals how the strain field from the dislocations in the defected layer leads to out-of-plane deformations, which in turn cause deformations of neighboring layers. Quantitative predictions are made for the defect-free energy of the multilayer stacks as compared to a defect-free system, which is shown to increase with the number of layers and system size. Furthermore, it is predicted that system defect energy saturates by roughly ten sheets in the stack, indicating the range of defect influence across the multilayer. Variations in stress field distribution and layer height profiles in different layers of the stack are also quantitatively identified.

Nanoscale ${\mathrm{W}}_{1-x}{\mathrm{Si}}_x$ layers with different Si content were deposited by magnetron sputtering on amorphous silicon layers. The structure and stress evolution during deposition were monitored in situ and in real time. Thus, it was possible to disentangle different origins of stress built-up (interface formation, phase formation, grain growth, and texture) on the nanoscale. It was found that the bcc phase with a composition-dependent texture forms at low Si content (less than 10% Si), but only above a critical thickness. At intermediate Si content $(13.9\% \text{and} 16.5\% \mathrm{Si})$, or low Si content and low thicknesses $(\lesssim 4.5 \mathrm{nm})$, the $\beta$ phase with A15 structure and coexisting phases (bcc or amorphous) form, while a single, amorphous phase is observed at high Si content $(\gtrsim 22\% \mathrm{Si})$. An A15 formation driven by impurities (O,C,N) was excluded by combined in situ x-ray photoelectron spectroscopy and ex situ x-ray diffraction measurements on a second sample series. Ab initio calculations of substitutional bcc and A15 ${\mathrm{W}}_{1-x}{\mathrm{Si}}_x$ alloys support the formation of A15 at higher Si content. The A15-containing interlayer should be taken into account when discussing the superconductivity of W/Si multilayers. The stress evolution during deposition of ${\mathrm{W}}_{1-x}{\mathrm{Si}}_x$ was correlated with the microstructure evolution, and compared to similar observations for ${\mathrm{Mo}}_{1-x}{\mathrm{Si}}_x$. Due to the crystalline phase (bcc/A15) and bcc texture ([111] and [110]) competition, the structure formation of ${\mathrm{W}}_{1-x}{\mathrm{Si}}_x$ shows a higher complexity. This explains the wide range of stress states (from tensile to compressive) observed after deposition of ${\mathrm{W}}_{1-x}{\mathrm{Si}}_x$. Nanoscale W-Si based stress-compensation layers could be employed for tailoring the stress state of nonepitaxial semiconductor devices.

Hydrous phases play a fundamental role in the deep-water cycle on Earth. Understanding their stability and thermoelastic properties is essential for constraining their abundance using seismic tomography. However, determining their elastic properties at extreme conditions is notoriously challenging. The challenges stem from the complex behavior of hydrogen bonds under high pressures and temperatures ($P,T\mathrm{s}$). In this study, we evaluate how advanced molecular dynamics simulation techniques can address these challenges by investigating the adiabatic elasticity and acoustic velocities of $\delta \text{−}\mathrm{AlOOH}$, a critical and prototypical high-pressure hydrous phase. We compared the performances of three methods to assess their viability and accuracy. The thermoelastic tensor was computed up to 140 GPa and temperatures up to 2700 K using molecular dynamics with a DeePMD machine-learning interatomic potential based on the SCAN meta-GGA functional. The excellent agreement with ambient condition single-crystal ultrasound measurements and the correct description of velocity changes induced by H-bond disorder-symmetrization transition observed at 10 GPa in Brillouin scattering measurements underscores the accuracy and efficacy of our approach.

In light of the recent research interest in low-dimensional bismuth structures as spin-active materials and topological insulators, we present a comprehensive characterization of the $\mathrm{Bi}/\mathrm{Au}\left(111\right)$ interface. The nuanced evolution of Bi phases upon deposition in ultrahigh vacuum (UHV) on a $\mathrm{Au}\left(111\right)$ surface is investigated from semidisordered clusters to few-layer $\mathrm{Bi}\left(110\right)$ thin films. Particular attention is devoted to the high-coverage, submonolayer phases, commonly grouped under the $(P\times \sqrt{3})$ nomenclature. We bring forth a new model, refining the current understanding of the $\mathrm{Bi}/\mathrm{Au}\left(111\right)$ interface and demonstrating the existence of submonolayer moiré superstructures, whose geometry and superperiodicity depend on their coverage. This tuneable periodicity paves the way for their use as tailored buffer and templating layers for epitaxial growth of thin films on $\mathrm{Au}\left(111\right)$. Finally, we clarify the growth mode of multilayer $\mathrm{Bi}\left(110\right)$ as bilayer-by-bilayer, allowing precise thickness control of anisotropically strained thin films. This holistic understanding of the structural properties of the material was enabled by the synergy of several experimental techniques, namely low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy and spectroscopy (STM, STS), and x-ray standing waves (XSW), further corroborated by density functional theory (DFT) simulations.

$Ln{M}_2{T}_8$-family materials have been proposed to be heavy-fermion systems with quasi-one-dimensional structures. We synthesized single crystals of ${\mathrm{CeFe}}_2{\mathrm{Ga}}_8$ and ${\mathrm{SmFe}}_2{\mathrm{Ga}}_8$ and systematically investigated their structural and magnetic properties. Both ${\mathrm{CeFe}}_2{\mathrm{Ga}}_8$ and ${\mathrm{SmFe}}_2{\mathrm{Ga}}_8$ exhibit an incoherent Kondo interaction between the localized $4f$ electrons and the conduction electrons at elevated temperatures. A short-range magnetic interaction of Fe ions was detected at low temperatures in magnetic measurements in ${\mathrm{CeFe}}_2{\mathrm{Ga}}_8$, while the Ce ions were found to be non-magnetic, which is a character of intermediate valence behavior. For ${\mathrm{SmFe}}_2{\mathrm{Ga}}_8$, magnetic and specific-heat measurements indicated an antiferromagneticlike phase transition occurring around 10 K, which is insensitive to magnetic fields. More analysis indicated that the antiferromagneticlike transition originates from the interaction of $\mathrm{S}{\mathrm{m}}^{3+}$ ions. Additionally, the large value of the Sommerfeld coefficient for ${\mathrm{SmFe}}_2{\mathrm{Ga}}_8$ suggests a heavy-fermion behavior in this compound. Our study of these two compounds provides insights into the ground state and magnetic structure of this series of heavy-fermion materials.

Point defects in semiconductors are attractive candidates for quantum information science applications owing to their ability to act as spin-photon interface or single-photon emitters. However, the coupling between the change of dipole moment upon electronic excitation and stray electric fields in the vicinity of the defect, an effect known as Stark shift, can cause significant spectral diffusion in the emitted photons. In this work, using first principles computations, we revisit the methodology to compute the Stark shift of point defects up to the second order. The approach consists of applying an electric field on a defect in a slab and monitoring the changes in the computed zero-phonon line (i.e., difference in energy between the ground and excited state) obtained from constraining the orbital occupations (constrained-DFT). We study the Stark shift of the negatively charged nitrogen-vacancy (NV) center in diamond using this slab approach. We discuss and compare two approaches to ensure a negatively charged defect in a slab and we show that converged values of the Stark shift measured by the change in dipole moment between the ground and excited states $\left(\mathrm{\Delta }\mu \right)$ can be obtained. We obtain a Stark shift of $\mathrm{\Delta }\mu =2.68\mathrm{D}$ using the semilocal GGA-PBE functional and of $\mathrm{\Delta }\mu =2.23\mathrm{D}$ using the HSE hybrid functional. These values are in good agreement with experimental results. We also show that modern theory of polarization can be used on constrained-DFT to obtain Stark shifts in very good agreement with the slab computations.