The fabrication of perovskite oxide free-standing films (membranes) by lift-off methods using water-soluble sacrificial layers such as ${\mathrm{Sr}}_3{\mathrm{Al}}_2{\mathrm{O}}_6$ is appealing because of the new possibilities that these membranes present over conventional epitaxial films. However, little is known about how the fabrication process itself, and in particular the exposure to water during the etching step, affects their properties. Here, we investigate how membranes of two perovskite archetypes, antiferroelectric $\mathrm{PbZr}{\mathrm{O}}_3$ and paraelectric $\mathrm{SrTi}{\mathrm{O}}_3$, are affected by this fabrication process. We find evidence that hydrogen penetrates the perovskite structure. Concomitant with this protonation, the functional properties also change, and both materials display ferroelectric-like behavior that is absent in bulk or in hydrogen-free films at room temperature. We also find that thermal annealing can be used to expel the hydrogen from the membranes, which henceforth recover their bulklike properties.

In this study, we unveil the remarkable tunability of electronic and magnetic properties in $\mathrm{NbO}{\mathrm{Cl}}_2$ nanoribbons through precise control of edge chemistry, structural reconstruction, and chemical passivation. By investigating nanoribbons oriented along both $x$ and $y$ directions, we reveal how subtle variations in edge termination and symmetry drive emergent phenomena such as edge-localized magnetism, half-metallicity, and unconventional bandgap modulation. Oxygen-rich edges foster spin-polarized flat bands near the Fermi level, enabling potential spin-filtering applications, while niobium-terminated edges exhibit robust metallicity with spin-split states. Structural reconstruction and hydrogen passivation are shown to be powerful tools for stabilizing these low-dimensional systems while selectively tuning their magnetic states either quenching or inducing magnetism depending on the configuration. Notably, wider nanoribbons defy typical quantum confinement trends, with enhanced magnetic interactions leading to unexpected bandgap expansion. These insights demonstrate how $\mathrm{NbO}{\mathrm{Cl}}_2$ nanoribbons serve as a versatile platform for engineering next-generation spintronic devices, offering pathways for chemically and structurally driven manipulation of magnetism and electronic transport at the nanoscale.

${\mathrm{Mn}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$ (MTO) is a magnetoelectric material with Ising-like antiferromagnetism (AFM) in which an applied magnetic field ($H$) induces electric polarization and an applied electric field produces magnetization. Here, we report results from our detailed investigations of the temperature ($T$) and $H$ dependence of magnetization ($M$) and heat capacity of MTO. These results show AFM ordering in MTO below $T_N \sim$ 102 K followed by additional transitions near $T_{S1} \sim$ 50 K and $T_{S2} \sim$ 20 K. The $M$ vs $H$ variations at 3 K show the presence of weak ferromagnetism (FM) below $T_{S1}$ superposed on AFM, with coercivity becoming zero for $T\ge T_{S1}$. This weak FM for $T\le T_{S1}$ is likely due to two inequivalent ${\mathrm{Mn}}^{2+}$ ions present in MTO. The magnetic susceptibility $\chi$ vs $T$ data for $T> T_N$ is used to determine two dominant AFM exchange constants $J_2/k_B$ = –11.3 K and $J_3/k_B$ = –22.9 K, which are in good agreement with those determined from the first-principles density-functional theory ($\mathrm{DFT}+U$) calculations. It is argued that the $H$-induced transition observed at 3 K at the critical field $H_c \sim$ 20 kOe is a spin flop transition whose surprising shift to higher $H$ values with increasing $T$ is explained in terms of $T$ dependence of anisotropic $\chi$, magnetic anisotropy, and exchange fields. The temperature dependence of magnetic specific heat and entropy shows the presence of short-range spin correlations ordering up to 140 K, a $\lambda$-type anomaly at $T_N$, and a broad anomalous peak near 40 K covering the region of $T_{S1}$ and $T_{S2}$. To further explore the nature of these transitions at $T_N, T_{S1}$, and $T_{S2}$, the $T$ dependence of various Raman modes of MTO was measured and compared with the lattice dynamics calculations from $\mathrm{DFT}+U$. For $T> T_N, T$ dependencies of the frequency and linewidth of the Raman modes are described by the three-phonon anharmonic approximation with considerable departures in these quantities observed at $T_N, T_{S1}$, and $T_{S2}$, which are then related to the strong spin-phonon coupling evident in MTO.

Photocatalytic water splitting has attracted considerable attention for renewable energy production. Since the first reported photocatalytic water splitting by titanium dioxide, this material remains one of the most promising photocatalysts, due to its suitable band gap and band-edge positions. However, predicting both of these properties is a challenging task for existing computational methods. Here, we show how Koopmans spectral functionals can accurately predict the band structure and level alignment of rutile, anatase, and brookite ${\mathrm{TiO}}_2$ using a computationally efficient workflow that only requires (a) a DFT calculation of the photocatalyst/vacuum interface and (b) a Koopmans spectral functional calculation of the bulk photocatalyst. The success of this approach for ${\mathrm{TiO}}_2$ suggests that this strategy could be deployed for assessing the suitability of novel photocatalyst candidates.

A Moment Tensor Potential (MTP) has been developed for the Cu–Ag binary alloy and its accuracy, transferability, and thermodynamic fidelity evaluated. The model was trained on a diverse dataset encompassing solid, liquid, and interfacial configurations derived from density functional theory (DFT) calculations. Benchmarking against experiment and DFT data demonstrated significant improvements over the widely used classical Embedded Atom Method (EAM) potential, particularly in predicting defect energetics, surface properties, and the eutectic phase diagram. Despite a slight underestimation of Ag's melting point, the MTP model achieved consistent accuracy across elemental and binary systems without direct fitting to high-temperature phase transitions. The predicted eutectic temperature and composition were found in close agreement with experimental observations. These results establish MTP as a robust framework for modeling immiscible metallic systems and pave the way for its integration into large-scale atomistic simulations where both fidelity and generalizability are essential.

Future high-power, high-frequency transistors may make use of high-Al-content AlGaN due to its large critical electric field and resulting potential for highly scaled devices. Since AlN is the most likely substrate for these devices, there is a significant lattice mismatch between the AlN substrate and lower-Al alloy layers needed for barriers, channels, and contacts. This work demonstrates fully coherent graded AlGaN heterostructures based on AlN templates, which could be implemented into future devices. We show the importance of well-controlled growth conditions, AlGaN layer thicknesses, and composition steps through transmission electron microscopy, atomic force microscopy, and high-resolution x-ray diffraction measurements to guide the epitaxial design of future generations of AlGaN-based transistors. We also emphasize the importance of careful analysis of high-resolution x-ray diffraction data in the context of a heterogeneous microstructure, such as one exhibiting crosshatch, in which there are simultaneously heavily dislocated and coherent crystalline regions in a thin layer.

We demonstrate quantum levitation controlled by Casimir forces acting between a polystyrene surface and a Teflon-coated metallic substrate immersed in a mixture of toluene and magnetite particles. This system experiences repulsion-attraction transitions in the Casimir interaction for distances where the effect is measurable. This Casimir trapping can be controlled by clever choices of metallic and ferrofluid materials, which are directly linked to the emergence of the trapping effect. Thermal and quantum contributions are investigated in detail, showing how the optical and magnetic properties of the ferrofluid and other materials affect the magnitude of the trapping and its distance range of observability.

We perform $\mathit{in} \mathit{situ}$ angle-resolved photoemission spectroscopy to investigate the effect of surface termination conversion on two-dimensional electron gas (2DEG) at the ${\mathrm{EuTiO}}_3$(001) surface. We successfully engineered ${\mathrm{EuTiO}}_3$ with nearly single ${\mathrm{TiO}}_2$ termination via epitaxial growth on ${\mathrm{TiO}}_2$-terminated ${\mathrm{SrTiO}}_3$, and ${\mathrm{EuTiO}}_3$ with nearly complete EuO termination by inserting a ${\mathrm{SrRuO}}_3$ buffer layer into the heterostructure. The orbital configuration of the 2DEG exhibits a strong dependence on the ${\mathrm{EuTiO}}_3$ termination, and this experimental observation matches our first-principles calculation results very well. Furthermore, we observe the termination dependence of a kink feature in $d_{xy}$ band. This finding implies that many-body interactions, and possibly magnetism, are influenced by the surface termination. Our study not only introduces a method to fabricate surface or interfacial 2DEG system, but also highlights the effect of termination conversion on magnetic 2DEG.

For large polarons, Fröhlich theoretically derived an increased effective mass and a decreased energy as compared to free charge carriers. These changes have hitherto eluded direct observation. Here, we report on the direct observation of large polaron formation after photoexcitation in BiOI nanoplatelets, a system known to host spatially separated e-h pairs. We employ time- and momentum-resolved photoemission electron microscopy with 50-fs pulses to monitor the dynamics of the conduction-band (CB) dispersion $E\left(k\right)$. Indeed, we observe a doubling of the effective mass accompanied by a decrease of the CB energy leading to an overall drop of 160 meV.

In this work, we report on large-scale molecular-dynamics (MD) simulations of displacement cascades in equiatomic NbMoTaW alloys at PKA energies ranging from 0.15 to 150 keV. We find defect production to be strongly dependent on recoil energy, scaling sublinearly up to 10 keV, and linearly thereafter. We find the sublinear regime to be defined by low values of surviving Frenkel pairs, typically found as isolated point defects or small defect clusters, while at higher recoil energies dense cascades become more frequent, leading to splitting into subcascades and the production of relatively large prismatic-dislocation loops with $\langle 111\rangle$ and $\langle 001\rangle$ Burgers vectors. These loops immobilize large fractions of defects, leading to a rapid growth of the number of surviving defects in the linear regime. We also anneal post-cascade defect configurations using object-kinetic Monte Carlo (OKMC) simulations to account for intracascade recombination on time scales not accessible to MD simulations. Cascade annealing is strongly temperature dependent, with the OKMC simulations only showing significant recovery at 1000 K but not below. Our results are in general agreement with existing published data for refractory concentrated alloys.

We develop a machine-learned interatomic potential for AlCrCuFeNi high-entropy alloys (HEA) using a diverse set of structures from density functional theory calculated including magnetic effects. The potential is based on the computationally efficient tabulated version of the Gaussian approximation potential method (tabGAP) and is a general-purpose model for molecular dynamics simulation of the HEA system, with additional emphasis on radiation damage effects. We use the potential to study key properties of AlCrCuFeNi HEAs at different compositions, focusing on the face-centered- and body-centered-cubic (fcc and bcc) phase stability. Monte Carlo swapping simulations are performed to understand the stability and segregation of the HEA and reveal clear FeCr and Cu segregation. Close to equiatomic composition, a transition from fcc to bcc is detected, following the valence electron concentration stability rule. Furthermore, we perform overlapping cascade simulations to investigate radiation damage production and tolerance. Different alloy compositions show significant differences in defect concentrations, and all alloy compositions show enrichment of some elements in or around defects. We find that, generally, a lower Al content corresponds to lower defect concentrations during irradiation. Furthermore, clear short-range ordering is observed as a consequence of continued irradiation.

Rare earth (RE)–free permanent magnets, as alternative substitutes for RE-containing magnets for sustainable energy technologies and modern electronics, have attracted considerable interest. We performed a comprehensive search for new hard magnetic materials in the ternary Fe-Co-Zr space by leveraging a scalable, machine learning–assisted materials discovery framework running on GPU-enabled exascale computing resources. This framework integrates a crystal graph convolutional neural network (CGCNN) machine learning (ML) method with first-principles calculations to efficiently navigate the vast composition-structure space. The efficiency and accuracy of the ML approach enable us to reveal 9 new thermodynamically stable ternary Fe-Co-Zr compounds and 81 promising low-energy metastable phases with their formation energies within 0.1 eV/atom above the convex hull. The predicted compounds span a wide range of crystal symmetries and magnetic behaviors, providing a rich platform for tuning functional properties. Based on the analysis of site-specific magnetic properties, we show that the ${\mathrm{Fe}}_6{\mathrm{Co}}_{17}{\mathrm{Zr}}_6$ compound obtained from our ML discovery can be further optimized by chemical doping. Chemical substitutions lead to a ternary ${\mathrm{Fe}}_5{\mathrm{Co}}_{18}{\mathrm{Zr}}_6$ phase with a strong anisotropy of ${\mathrm{K}}_1=1.1\mathrm{MJ}\text{/}{\mathrm{m}}^3$ and a stable quaternary magnetic ${\mathrm{Fe}}_5{\mathrm{Co}}_{16}{\mathrm{Zr}}_6{\mathrm{Mn}}_4$ compound.

The interlayer exchange coupling in Fe/MgO(001) superlattices is found to increase exponentially with decreasing temperature. Around 150 K, the field-induced response changes from discrete switching—governed by field-driven domain propagation—to a collective rotation of the magnetic layers. This transition is accompanied by a change in the magnetic ground state from ${180}^{\circ }$ (antiferromagnetic) to ${90}^{\circ }$ alignment between adjacent Fe layers. These effects are argued to arise from quantum-well states, defined by the total thickness of the samples.

The anomalous Nernst effect (ANE), a thermoelectric (TE) phenomenon that generates a voltage perpendicular to both temperature gradients and spontaneous magnetization, has attracted interest in energy harvesting applications. However, its practical implementation remains limited by low TE conversion efficiency. Here, we investigated strain-induced enhancement of ANE in a $\mathrm{D}{0}_3$-type Heusler compound $\mathrm{F}{\mathrm{e}}_3\mathrm{Si}$ using first-principles calculations. The transverse TE conductivity improved approximately 50-fold compared to the unstrained condition, due to the $4\%$ compressive strain loading on the (111) plane. The electronic structure analysis revealed that the improvement stems from the nodal line shift closer to the Fermi energy under compressed strain. Strain engineering offers a promising approach to manipulate the topological electronic structure, such as nodal lines and Weyl nodes, which are the origin of ANE, and thus enhance TE performance. These results suggest new design principles for high-performance TE devices.

Currently, the realization and control of anomalous valley Hall effect (AVHE) in two-dimensional antiferromagnetic (AFM) systems are predominantly achieved through optical excitation, which hinders its practical applications. Here, we propose a strategy to overcome this limitation by inserting a valley-active AFM layer between two ferromagnetic (FM) semiconductor layers. Using $\mathrm{Cr}{\mathrm{Cl}}_3-\mathrm{VSi}{\mathrm{S}}_3-\mathrm{Cr}{\mathrm{Cl}}_3$ heterotrilayer as a model system, our first-principles calculations reveal that interfacial proximity coupling can introduce intrinsic sublattice-asymmetric exchange field. This field can break the $\mathit{PT}$ symmetry and lift the spin degeneracy of valleys in the AFM layer while preserving its intrinsic valley polarization, thereby inducing a pronounced AVHE. Crucially, the sublattice-asymmetric exchange field can be reversed through flipping the magnetization orientation of the FM layers, resulting in reversible static control of AVHE without altering the AFM Néel order. These findings establish an alternative paradigm for controlling AVHE in AFM materials and advance the field of antiferromagnet-based valleytronics.

Quasi-one-dimensional GaSeI nanochain with a noncentrosymmetric helical chain structure have recently been synthesized, offering a unique platform for exploring mechanical and thermal properties in low-dimensional materials. Here, we develop a neuroevolution potential (NEP) for GaSeI nanochain based on ab initio molecular-dynamics (AIMD) simulations, enabling systematic investigation of their mechanical response and lattice thermal transport. Stress-strain analysis reveals that GaSeI nanochain exhibits mechanical strength comparable to carbon nanotubes, with ultimate stress approaching that of graphene, indicating that, despite distinct bonding mechanisms, the material possesses high structural stability. Nonequilibrium molecular-dynamics (NEMD) calculations show that the lattice thermal conductivity is lower than that predicted by the phonon Boltzmann transport equation, due to the inherent inclusion of higher-order phonon scattering in NEMD. Thermal conductivity decreases modestly with increasing tensile strain, yet the reduction is far smaller than that observed in typical one-dimensional materials, such as carbon nanotube. This behavior arises from the weaker polar-covalent nature of Ga-Se bonds, which can buffer structural perturbations via local bond-angle adjustments, thereby maintaining robust phonon transport. These findings demonstrate that GaSeI nanochain possess both excellent mechanical stability and strain-insensitive thermal conductivity, suggesting their potential application in thermal management of flexible, stretchable, and deformable devices.