Using isoconfigurational ensemble simulations, we investigate the diffusion direction of individual particles in liquids in two dimensions. We find that the particle diffusion direction on the cage-jumping timescale is not random in the supercooled regime, and the diffusion anisotropy increases with decreasing temperature. Analyses of the simulations and colloidal experiments show that the diffusion anisotropy originates from the rise of the anisotropic local potential energy landscape. Particles prefer to move in directions with soft local stiffness during structural rearrangements. The structural evolution in supercooled liquids can thus be probabilistically predicted from the potential energy landscape that is determined by local structures.

We report evidence for the formation of niobium hydride phase within niobium films on silicon substrates in superconducting qubits fabricated at Rigetti Computing. For this study, we combined complementary techniques—including room-temperature and cryogenic atomic force microscopy (AFM), synchrotron x-ray diffraction, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS)—to directly reveal the existence of niobium hydride precipitates on the surface of superconducting qubits. Upon cryogenic cooling, we observed variation in the size and morphology of the hydrides, ranging from small (∼5 nm) irregular shapes to large (∼10–100 nm) domains within the Nb grains, which were fully converted to niobium hydrides. Since niobium hydrides are nonsuperconducting and can easily change in size and location upon different cooldowns to cryogenic temperature, our finding highlights a previously unknown source of decoherence in superconducting qubits. This contributes to quasiparticle losses, offering a potential explanation for changes in qubit performance upon cooldowns. Finally, by leveraging the RF performance of a 3D bulk Nb resonator, we quantify RF dissipation in a superconducting qubit caused by hydrogen concentration variation, and propose a practical engineering pathway to mitigate the formation of Nb hydrides for superconducting qubit applications.

Although phase field methods are widely recognized as valuable tools for modeling and understanding microstructural changes in nonequilibrium systems, their predictive capabilities have suffered from the difficulty that lies in defining a time scale. We have therefore developed a predictive method for modeling the kinetics with which a nonequilibrium conservative system reaches thermodynamic equilibrium. The method, which couples effective medium theory and phase field is self-consistent, making it fully predictive, providing atomic diffusion properties are sufficiently well known. We validate the method by studying the demixing kinetics in a wide range of binary alloys but focusing on Fe-Cr, an archetypal system against which phase field applications are often assessed. The extension of the method to nonconservative systems is straightforward.

Two-dimensional magnetic materials exhibit strong magneto-optic effects and high tunability by electrostatic gating, making them very attractive for new magneto-photonic devices. Here, we characterize the magneto-optic Kerr effect (MOKE) spectrum of thin ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ from 1.13 to 2.67 eV, and demonstrate electrostatic control over its magnetic and magneto-optic properties. The MOKE spectrum exhibits a strong feature around 1.43 eV, which we attribute to a magnetic-exchange-split excitonic state in ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$, in agreement with ab-initio calculations. The gate dependence of the MOKE signals shows that the magneto-optical efficiency—rather than the saturation magnetization—is affected by electrostatic gating. We demonstrate a modulation of the magneto-optical strength by over 1 mdeg, with some wavelengths showing a modulation of 65% of the total magneto-optical signals, opening the door for efficient electrical control over light polarization through two-dimensional magnets. Our findings bring forward the fundamental understanding of magneto-optic processes in two-dimensional magnets and are highly relevant for the engineering of devices that exploit excitonic resonances for electrically tunable magneto-photonic devices.

We propose a protocol of low-temperature, strain-tuned re-entrant metal-insulator transition, and crossover between strongly correlated line-graph lattices (Lieb and Kagome). Using a nonperturbative numerical approach, we demonstrate that an applied shear strain stabilizes a metallic phase cradled in between a gapped magnetic insulator and a gapless flat band transiently localized insulator, facilitating the Lieb/Kagome interconversion. Our results on transport signatures exhibit variable scaling exponents for electrical resistivity and optical conductivity, providing clear evidence of non-Fermi liquid physics. We also define a strain-dependent thermal scale to quantify the crossover between the non-Fermi liquid and bad metal phases.

Recently, Lai and Schuh [Phys. Rev. Lett. 26, 015701 (2021)] used a direct electric field to induce phase transformation in dielectric zirconia. This martensitic phase transformation from the monoclinic to the tetragonal phase was described by a thermodynamic model that depends on the susceptibility difference between the phases. Here we explore the anisotropic nature of the susceptibility difference for optimal single-crystal orientations. For a monoclinic single crystal subjected to a uniaxial applied electric field, we find that the orientation dependence of the susceptibility difference is dominated by the tetragonal phase in the 24 possible variant combinations. This tetragonal dominance results from the greater anisotropy of electric susceptibility in the tetragonal phase. In contrast, the monoclinic phase dominates the orientation dependence of the transformation strain. Conveniently, maximum transformation strain can be achieved in orientations that also have relatively low required electric field to induce the phase transformation; these always occur by the “B” correspondence orientation relationship. In addition, the temperature dependence of the thermodynamic model is such that these optimal single-crystal orientations allow for phase transformations at lower temperatures. A simple comparison to a homogenized, randomly oriented polycrystal shows that the best polycrystals perform about as well as the least optimal single-crystal orientations. Thus, optimal orientation of a single crystal can provide significantly improved conditions for electrically induced phase transformations in zirconia.

Isentropic magnetic compression and ab initio calculations on the compressibility and equation of state (EOS) for solid carbon dioxide were performed up to pressures of 540 GPa and 1.6 TPa, respectively. A method of isentropic compression by pressure of an ultrahigh magnetic field from an explosive magnetocumulative generator MC-1 was applied for the dynamic compression of solid ${\mathrm{CO}}_2$ samples to multimegabar pressures, with the simultaneous x-ray imaging of the compressed samples. An amplified magnetic field of the MC-1 generator plays the role of an intermediate medium converting the detonation waves into the smoothly increasing compression waves, thus achieving a high degree of isentropic conditions of the sample compression. This method is especially unique in achieving 500–700 GPa pressures in highly compressible substances, with sample heating only to $\sim 1000$ K, whereas known dynamic shock-wave methods do not allow for large compression in solids due to strong heating of the sample. As a result, eight points on the ${\mathrm{CO}}_2$ compressibility curve were obtained at pressures from 47 to 540 GPa. The maximum density of the ${\mathrm{CO}}_2$ sample achieved at this pressure was $6.87\mathrm{g}/\mathrm{c}{\mathrm{m}}^3$. This corresponds to the highest compression ratio ever achieved for solid ${\mathrm{CO}}_2$ with $\rho /{\rho }_0=4.24$. The experimental results were compared with theoretical calculations of the EOSs of ${\mathrm{CO}}_2$ phases and showed their close agreement. This indicates that covalent polymeric phases of ${\mathrm{CO}}_2$ with crystal structures corresponding to theoretical calculations were obtained in the magnetic compression experiments. Accompanying first-principles theoretical calculations were carried out on solid ${\mathrm{CO}}_2$ phases at pressures up to 1.6 TPa and temperatures up to 5000 K in the quasiharmonic approximation. It was established that transition to phases with a sixfold coordination of carbon occurs at a pressure of about 1 TPa. No conductive solid phases were detected in the experiments or in calculations. The theoretical calculations also do not confirm dissociation of ${\mathrm{CO}}_2$ into carbon and oxygen. The obtained data clarify the compressibility and electrical conductivity of solid carbon dioxide at low temperatures and ultrahigh pressures and provide opportunities for constructing a wide-ranging EOS for this substance.

Cobalt-free high-entropy alloys have garnered interest for nuclear structural applications due to their good mechanical performance, thermal stability, and resistance to radiation-induced degradation, while avoiding long-lived Co radioisotopes. This study presents an experimental and computational investigation of the plastic deformation behavior of a nonequatomic CrMnFeNi alloy, designed to maintain a stability of fcc phase in a large domain of temperatures and to balance stacking fault (SF) energies for enhanced strain hardening and ductility. Tensile tests reveal a temperature-dependent reduction in mechanical strength, attributed to thermally activated deformation mechanisms and microstructural evolution. Molecular dynamics simulations of single- and polycrystals capture dislocation activity, SF formation, and twin nucleation as a function of strain and temperature. Electron backscatter diffraction confirms twin formation and grain boundary activity. The Schmid factor mapping is drawn to interpret local slip activity and anisotropic deformation behavior. The absence of Co leads to enhanced high-temperature strength compared to the Cantor alloy.

Density functional theory (DFT) calculations, within the virtual crystal alloy approximation, are performed, along with the development of a Landau-type model employing a symmetry-allowed analytical expression of the internal energy and having parameters determined from first principles, to investigate properties and energetics of ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$ ferroelectric nitrides in their hexagonal forms. These DFT computations and this model predict the existence of two different types of minima, namely, the fourfold-coordinated wurtzite (WZ) polar structure and a five-fold coordinated paraelectric hexagonal phase (denoted as H5), for any Sc composition up to 40%. The H5 minimum progressively becomes the lowest-energy state within hexagonal symmetry as the Sc concentration increases from 0 to 0.4. Furthermore, the model points to several key findings. Examples include the crucial role of the coupling between polarization and strains to create the WZ minimum, in addition to polar and elastic energies, and that the origin of the H5 state overcoming the WZ phase as the global minimum within hexagonal symmetry when increasing the Sc composition mostly lies in the compositional dependency of only two parameters—one linked to the polarization and another one being purely elastic in nature. Other examples are that forcing ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$ systems to have no or a weak change in lattice parameters when heating them allows us to reproduce their finite-temperature polar properties well and that a value of the axial ratio close to that of the ideal WZ structure implies a large polarization at low temperatures but not necessarily at high temperatures because of the ordered-disordered character of the temperature-induced formation of the WZ state. Such findings should allow for a better fundamental understanding of (Al,Sc)N ferroelectric nitrides, which may be used to design efficient devices having, e.g., low operating voltages.

Two-dimensional multiferroics, especially for ferromagnetic–ferroelectric materials, offer pivotal candidates for advancing fields such as nonvolatile information storage and spintronic devices. However, the mutual competition mechanism between ferroelectricity and magnetism leads to the scarcity of 2D multiferroics, severely limiting their practical deployment. Element substitution was considered as a viable engineering to bring in multiferroicity by tuning the electronic structures, but the complexity of substitution sites and the trial-and-error” approach result in low efficiency for this approach. Herein, we present a machine learning-assisted element substitution strategy to efficiently explore multiferroics in element substituted 2D transition metal dichalcogenides (TMD). By graph neural networks trained on a spin exchange interaction graph dataset, we developed a magnetism model, achieving rapid magnetism prediction with 81% cross-validation accuracy. Using this model to predict and screen the magnetism in the element substituted ferroelectric phase d1T-$\mathrm{M}{X}_2$ of 2D TMD, we identify five candidates d1T-$\mathrm{Mo}{Y}_2\text{−}X$ ($X$ = Ni, Fe, Zr, Cr; $Y$ = S, Te) in which substitution-induced magnetism can couple with ferroelectricity to form 2D multiferroics. Taking the d1T-${\mathrm{MoS}}_2$-Fe system, we expound its magnetic mechanisms and magnetic tunnel junction, revealing that the origin of magnetism lies in the $d$ orbitals of off-centered Fe ions and possessing nonvolatile magnetoelectricity applications. This work provides a robust machine-learning-assisted method for predicting magnetism and paves a way for more efficient discovery of transition-metal-substituted 2D multiferroics.

Solidification control is crucial in manufacturing technologies, as it determines the microstructure and, consequently, the performance of the final product. Investigating the mechanisms occurring during the early stages of nucleation remains experimentally challenging as it initiates on nanometer length and subpicoseconds time scales. Large scale molecular dynamics simulations using machine learning interatomic potential with quantum accuracy appears the dedicated approach to complex, atomic level, multidimensional mechanisms with local symmetry breaking. A potential trained on a high-dimensional neural network on density functional theory-based ab initio molecular dynamics (AIMD) trajectories for liquid and undercooled states for Al-Si binary alloys enables us to study the nucleation mechanisms occurring at the early stages from the liquid phase near the eutectic composition. Our results indicate that nucleation starts with Al in Al-rich conditions and with Si in Si-rich conditions. Whereas Al nuclei grow in a globular shape, Si ones grow with polygonal faceting, whose underlying mechanisms are further discussed.

The magnetic ground states in crystalline systems are significant for both fundamental condensed-matter physics and practical materials engineering. Marcasite ${\mathrm{FeTe}}_2$, characterized as a small-gap semiconductor, exhibits anomalous magnetic behaviors in low-temperature experiments. In this study, first-principles density-functional theory calculations combined with scanning-tunneling microscopy/spectroscopy are employed to investigate the magnetic ground state of marcasite ${\mathrm{FeTe}}_2$. It is revealed that the competition between crystal-field splitting and on-site Coulomb repulsion plays the key role in the formation of localized magnetic moments in ${\mathrm{FeTe}}_2$. The ground state of ${\mathrm{FeTe}}_2$ bulk is confirmed to be nonmagnetic, while the magnetic responses of ${\mathrm{FeTe}}_2$ observed at low temperatures are suggested to be related to the magnetic Fe atoms on the crystal surfaces. Our work proposes a straightforward competing mechanism for determining ground-state magnetism of various localized-moment crystalline systems.

We explore the possibility of modification of the magnetic properties of flux-grown icosahedral Al-Cu-Fe quasicrystals by individual and combined doping with Nd and Eu. Different dopants alter the Cu/Fe ratio of the icosahedral phase. In all three cases, the electron density is concentrated in even- and odd-parity vertices and even-parity body center of the hypercubic unit cell, which is consistent with the F-type icosahedral lattice of similar systems. Nd-doping is correlated with higher occupancy, probably with denser Cu or Fe atoms, of the even-parity body center of the six-dimensional unit cell. Doping with one lanthanide produces a semihard magnet, while the sample doped with both Nd and Eu shows soft magnetic properties. The highest observed remanence and saturation magnetization were achieved via Eu doping; $\mathrm{Nd}+\mathrm{Eu}$ yields half that value, and Nd only is even lower. Negative Curie-Weiss temperatures indicate strong antiferromagnetic long-range ordering with effective magnetic moments much smaller than expected for the Fe content. Comparison of the effective anisotropy energy distribution versus angle and magnetic field revealed the easy magnetization direction along preferred high-symmetry axes. The appearance of both $3\theta$ and $5\theta$ Fourier coefficients in the description of the angular dependence of torque at any applied magnetic field indicates that the anisotropic magnetic response of the quasicrystal has different symmetry than what would be expected for cubic crystalline magnetic materials with linear or cubic anisotropy.

With a surge of interest in spintronics, the manipulation and detection of colossal magnetoresistance in quasi-two-dimensional layered magnetic materials have become a key focus, driven by their relatively scarce occurrence compared to giant magnetoresistance and tunneling magnetoresistance. This study presents an investigation into the desired colossal magnetoresistance, achieved by introducing magnetic frustration through Te doping in quasi-two-dimensional antiferromagnet ${\mathrm{Cr}}_2{\mathrm{Se}}_3$ matrix. The resulting ${\mathrm{Cr}}_{0.98}{\mathrm{SeTe}}_{0.27}$ exhibits cluster glass-like behavior with a freezing temperature of 28 K. Magnetotransport studies reveal a significant negative magnetoresistance of up to 32%. Additionally, angle-dependent transport measurements demonstrate a magnetic field-induced transition from positive to negative resistance anisotropy, suggesting a magnetic field-driven alteration in the electronic structure of this narrow band gap semiconductor, a characteristic feature of the colossal magnetoresistance effect. This behavior is further corroborated by density functional theory calculations. This systematic investigation provides a crucial understanding of the control of colossal magnetoresistance in quasi-two-dimensional materials via competing exchange interactions.

We present a first-principles quantum statistical theory of dislocation motion based on discrete lattice dynamics and the Keldysh nonequilibrium formalism. By treating the dislocation as a moving source coupled to the phonon field through exact Kanzaki forces, we derive a universal memory kernel that captures all phononmediated dissipation mechanisms without adjustable parameters. The theory naturally produces the experimentally observed drag regimes: linear phonon wind at low velocities, quadratic radiation damping at intermediate speeds, and finite drag enhancement near the speed of sound. Crucially, we demonstrate that the elastodynamic prediction of an infinite sound barrier is an artefact of continuum approximations; the discrete lattice structure and anharmonic phonon interactions regularize all singularities, permitting transonic motion at finite stress. Through systematic reduction via conserving approximations, we obtain practical mobility laws suitable for crystal plasticity and dislocation dynamics simulations. These take the form of either steady state algebraic relations or minimal differential systems that capture memory effects while adding negligible computational cost. All parameters derive directly from harmonic and anharmonic force constants, enabling predictive modeling across ten orders of magnitude in strain rate. Application to fcc and bcc metals yields drag coefficients and relaxation times in good agreement with molecular dynamics and available experiments, validating the approach. This work establishes a microscopic foundation for dislocation mobility and provides a pathway from atomistic properties to continuum plasticity without empirical fitting.

The electronic properties of the Ca/Sr and Mn site substitution of ${\mathrm{CaMnGe}}_2{\mathrm{O}}_6$ and ${\mathrm{SrMnGe}}_2{\mathrm{O}}_6$ clinopyroxene systems have been investigated by ab initio calculations within the density functional theory (DFT) framework, using on-site Hubbard $U$ to describe the highly correlated Mn $3d$ states and a hybrid exchange-correlation functional to obtain the energy band-gap values. Compositions such as ${(\mathrm{Ca},\mathrm{Sr})}_{1-x}{\mathrm{Cd}}_x{\mathrm{MnGe}}_2{\mathrm{O}}_6$ and $(\mathrm{Ca},\mathrm{Sr}){\mathrm{Mn}}_{1-x}{\mathrm{Cd}}_x{\mathrm{Ge}}_2{\mathrm{O}}_6$ (where $x=0.125,0.25$) are predicted to be stable. Also, we proved that implanted Cd impurity could indeed replace either the Ca/Sr or the Mn sites in the crystalline structures. These findings were obtained by combining first principles electric field gradient calculations, using a supercell scheme, with experimental time-differential perturbed angular correlation results. Additionally, DFT calculations showed that Cd substitution is expected to lead to a reduction in the band-gap width. Cd-doped systems were successfully synthesized and experimental results evidencing opportunities for potential band-gap engineering are reported.

We report the successful growth of stoichiometric, epitaxial ytterbium nitride (YbN) thin films via molecular beam epitaxy under ultrahigh vacuum conditions using activated nitrogen supplied by a plasma source. Through systematic optimization of the growth parameters, we achieved high-quality YbN films with excellent crystallinity and a well-defined (100) out-of-plane orientation on MgO(100) and ${\mathrm{LaAlO}}_3$(100) substrates, as determined by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction. $\mathit{In}$ situ photoelectron spectroscopy results unambiguously demonstrate the semiconducting character of YbN and the fully trivalent valence state of the Yb ions. Using the photon-energy dependence of the valence band spectra we were able to reveal a significant hybridization between the $\mathrm{Yb}4f$ and $\mathrm{N}2p$ states.

Lattice thermal conductivity (${\kappa }_L$) is a key physical property governing heat transport in solids, with direct relevance to thermoelectrics, thermal barrier coatings, and heat management applications. However, while experimental determination of ${\kappa }_L$ is challenging, its theoretical calculation via ab initio methods particularly using density functional theory (DFT) is computationally intensive, often more demanding than electronic transport calculations by an order of magnitude. In this work, we present a machine learning (ML) approach to predict ${\kappa }_L$ with DFT-level accuracy over a wide temperature range (100–1000 K). Among various models trained on DFT-calculated data obtained from literature, the Extra Trees Regressor (ETR) yielded the best performance on log-scaled ${\kappa }_L$, achieving an average $R^2$ of 0.9994 and a root mean square error (RMSE) of 0.0466 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. The ETR model also generalized well to 12 previously unseen (randomly chosen) low and high ${\kappa }_L$ compounds with diverse space group symmetries, reaching an $R^2$ of 0.961 against DFT benchmarks. Notably, the model excels in predicting ${\kappa }_L$ for both low- and high-symmetry compounds, enabling efficient high-throughput screening. We also demonstrate this capability by screening ultralow and ultrahigh ${\kappa }_L$ candidates among 960 half-Heusler compounds and 60 000 ICSD compounds from the aflow database. This result shows reliability of model developed for screening of potential thermoelectric materials. ${\kappa }_L$ predictions of few low ${\kappa }_L$ screened compounds are also verified with their DFT results. At the end, we have tested the model's prediction ability on systems that have experimental ${\kappa }_L$ available that shows the model's ability to search material that has desirable experimental ${\kappa }_L$ for thermoelectric applications.

Motivated by the experimental synthesis of the first ternary penta-PdPSe sheet [P. Li, et al., Adv. Mater. 33, 2102541 (2021)], we investigate its high-order phonon scattering and phonon coherence, along with their impact on the lattice thermal conductivity using first-principles calculations combined with the unified theory of thermal transport. The penta-PdPSe sheet is semiconducting with an indirect band gap of 1.94 eV at the HSE06 level. Our calculated results reveal that four-phonon scattering plays an important role in suppressing the lattice thermal conductivity. When four-phonon scattering is considered, the particle-like thermal conductivity ${\kappa }_L^P$ at 300 K is reduced by 54.70% along the $x$-direction and 59.05% along the $y$-direction. This reduction is primarily due to the strong scattering of acoustic phonons, which contributes approximately 88.50% to the particle-like lattice thermal transport. The phonon lifetime of acoustic modes of phonon is greater than the Wigner limit in time, resulting in a small contribution from phonon coherent transport. The total lattice thermal conductivity, incorporating both phonon scattering and coherence effects, exhibits anisotropic values of 6.20 $\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ along the $x$-direction and 7.68 $\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ along the $y$-direction at 300 K. The low lattice thermal conductivity arises from the large mass contrast between Pd and P/Se atoms, weak interatomic bonding, and puckered pentagonal geometry, which collectively enhance anharmonicity and phonon scattering. Our work provides new insights into the low lattice thermal transport properties of the first synthesized ternary penta-sheet.