Topological insulators and skyrmion-hosting, chiral magnetic multilayers are two well-explored areas of modern condensed matter physics, each offering unique advantages for spintronics applications. In this paper, we demonstrate the optimization process for the growth of a ${\mathrm{Bi}}_2{\mathrm{Se}}_3/\text{buffer}/{[\mathrm{Pt}/\mathrm{CoB}/\mathrm{Ru}]}_{\times N}$ heterostructure that combines these two material classes: the ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ epilayer was grown by molecular beam epitaxy before transfer under ultrahigh vacuum to a separate growth chamber where the polycrystalline metallic multilayer was sputter deposited. The structure of the samples was characterized by cofitted x-ray and polarized neutron reflectometry measurements and scanning transmission electron microscopy. Polarized neutron models and standard magnetometry show that a buffer layer exceeding a critical thickness is required to obtain the desired uniform, perpendicular magnetic anisotropy in every magnetic layer in the multilayer. Samples with both Ta and Mo buffers were used requiring thicknesses of 1.5 and 0.9 nm, respectively. In minimizing the ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ terracing, buffered samples yield well-defined, out-of-plane, magnetic domains suitable for spin-orbit torque-induced manipulation as determined by x-ray photoemission electron microscopy.

Transition metal oxides exhibit a wide range of tunable electronic properties arising from the complex interplay of charge, spin, and lattice degrees of freedom, governed by their $d$ orbital configurations, making them particularly interesting for oxide electronics and (electro)catalysis. Perovskite oxide heterointerfaces offer a promising route to engineer these orbital states. In this work, we tune the $\mathrm{Co}3d$ orbital occupancy in ${\mathrm{LaCoO}}_3$ from a partial $d^7$ to a partial $d^5$ state through interfacial engineering with ${\mathrm{LaTiO}}_3$, ${\mathrm{LaMnO}}_3$, ${\mathrm{LaAlO}}_3$, and ${\mathrm{LaNiO}}_3$. Using x-ray absorption spectroscopy combined with charge transfer multiplet calculations, we identify differences in the Co valence and spin state for the series of oxide heterostructures. ${\mathrm{LaTiO}}_3$ and ${\mathrm{LaMnO}}_3$ interfaces result in interfacial charge transfer towards ${\mathrm{LaCoO}}_3$, resulting in a partial $d^7$ orbital occupancy, while a ${\mathrm{LaNiO}}_3$ interface results in a partial Co $d^5$ occupancy. Strikingly, a ${\mathrm{LaAlO}}_3$ spacer layer between ${\mathrm{LaNiO}}_3$ and ${\mathrm{LaCoO}}_3$ results in a Co $d^6$ low-spin state. These results indicate that the Co spin state, like the valence state, is governed by the interfacial environment. High-resolution scanning transmission electron microscopy imaging reveals a clear connection between strain and spin configuration, emphasizing the importance of structural control at oxide interfaces. Overall, this work demonstrates that interfacial engineering simultaneously governs orbital occupancy and spin state in correlated oxides, advancing spin-engineering strategies in correlated oxides and offering new insights for the rational design of functional oxide heterostructures.

Three-dimensional printing of advanced functional materials via direct ink writing requires the design and processing of soft solids or yield stress materials with high solids concentrations. The deformation, flow, and microstructure evolution of such complex soft materials are central in additive manufacturing extrusion technologies. In this study, we investigate both bulk properties and microscopic dynamics using rheo-microscopy, particle tracking, and birefringence mapping. This work presents an integrated framework that maps bulk rheology to local spatiotemporal heterogeneities during yielding of soft materials by combining oscillatory rheology experiments with simultaneous in situ imaging. Using a Pluronic F127 hard gel matrix with increasing concentrations of silica fillers as a model for direct ink writing formulations, we quantify the evolution of deformation pathways under large-amplitude oscillatory shear tests with increasing concentration $\left(\mathrm{\Phi }\right)$. Mapping local events onto bulk rheological metrics unveils a consistent trend from a matrix-dominated to a filler-dominated deformation regime. At low concentrations $(\mathrm{\Phi }\lesssim 0.31)$, the matrix dominates the yielding mechanism, leading to an affine-banding-fracture pathway. However, at high concentrations $(\mathrm{\Phi }>0.31)$, the filler-dominated system undergoes multiple local events under small deformations, from which cracks propagate and fracture the material into yielded and solid like regions. This work reconciles bulk and local observations in a flow regime map for particle suspensions in a gel matrix, highlighting when a soft material exhibits the desired affine flow and when it undergoes catastrophic failure. The results demonstrate that the deformation of highly concentrated composites is complex, where heterogeneous yielding and fracture coexist and negatively impact printability and shape fidelity. The experimental evidence presented in this work provides a timely avenue toward understanding the heterogeneous deformation and flow of complex soft materials, which play a critical role in a wide breadth of applications beyond 3D printing.

Strain and domain engineering offer powerful routes to control phase and domain stability in ferroelectric thin films. While most studies have focused on (100)-oriented growth, the impact of lower-symmetry orientations remains underexplored. We address this knowledge gap with first-principles-based molecular dynamics simulations for the example of prototypical ferroelectric perovskites under (110) strain. Epitaxial (110) strains may indeed outperform the widely studied (100) orientation, as even modest strain values stabilize a diverse set of metastable nanoscale states with potential high functional tunability. In this regime, the films exhibit multidomain configurations with domain wall normals oriented along the clamped in-plane or the relaxed out-of-plane directions and heterophases in ${\mathrm{BaTiO}}_3$ and ${\mathrm{KNbO}}_3$. Besides, complex superdomain patterns and antiferroelectriclike domains are observed in ${\mathrm{PbTiO}}_3$. These metastable nanoscale configurations may allow for large reversible responses.

Shear bands lie at the root of fracture initiation in bulk metallic glasses and amorphous polymers. For silicate glasses, in contrast, studies have largely emphasized permanent volumetric strain, commonly referred to as densification. Here, we systematically investigate indentation-induced fracture in two distinct families of aluminoborosilicate glasses. The results demonstrate that plastic shear flow plays a decisive role in governing fracture initiation. In addition, molecular dynamics simulations reveal a pronounced composition dependence of softening associated with plastic shear flow, closely mirroring the experimentally observed propensity for strain localization. We conclude that silicate glasses conform to a universal pattern of rupture initiation governed by the localization of shear-deformation, aligning with a broad range of amorphous materials, including bulk metallic glasses and glassy polymers.

High-entropy alloys provide an ideal platform for investigating superconductivity in the presence of extreme chemical disorder, lattice distortion, and magnetic impurity effects. Herein, we report a systematic study of the structural, normal-state, and superconducting-state properties of ${\left(\text{TiVTa}\right)}_{0.6}{\text{Nb}}_{0.4-x}{\text{Cr}}_x$ high-entropy alloys with $x=0$, 0.05, and 0.20. All compositions crystallize in a single-phase body-centered-cubic structure, with space group Im-$3m$. Our detailed analysis includes magnetization, resistivity, and specific-heat capacity measurements. The superconducting transition temperature is progressively suppressed from 4.68 to 2.59 K and the upper critical field is decreased from 5.77 to 3.87 T with increasing Cr content in the structure. Heat capacity measurements confirm $s$-wave weak-coupling superconductivity with a superconducting gap within the BCS limit in all the materials. The suppression of transition temperature follows Abrikosov-Gor'kov behavior, identifying magnetic impurity scattering from Cr as the dominant pair breaking mechanism. First-principles calculation reveals severe local lattice distortion characterized by a large atomic size mismatch $\delta =5.5\%$ and a substantial average atomic displacement $(\mathrm{\Delta }d=0.22\AA )$. The interatomic distance distribution exhibits broadened coordination shells with partially filled gaps between nearest-neighbor shells, reflecting strong deviations from ideal lattice positions while retaining long-range crystalline order.

We report comprehensive thermodynamic and neutron scattering measurements on the $S=3/2$ antiferromagnet ${\mathrm{Cs}}_2{\mathrm{CoI}}_4$, a member of the thoroughly studied family of frustrated magnets ${\mathrm{Cs}}_{2}M{X}_4$ ($M=\mathrm{Cu}$, Co, Ru, $X=\mathrm{Br}$, Cl, I, O). Unlike previously studied members, ${\mathrm{Cs}}_2{\mathrm{CoI}}_4$ undergoes a structural phase transition, for which we determine the low-temperature crystallographic structure. The resulting symmetry reduction strongly affects both the magnetic exchange interactions and single-ion anisotropy. Despite the large parameter space, we propose a minimal magnetic Hamiltonian that reasonably captures the observed excitation spectrum, analyzed using extended SU(4) linear spin-wave theory.

Chemical substitution in crystalline quantum materials is a powerful way to explore the consequences of strong spin-orbit coupling on their structural and electronic properties. In this work, we present an investigation of thin films of the $\mathrm{La}{Pn}_2(Pn=\mathrm{Sb},\mathrm{Bi})$ class of layered square-net intermetallics. We report the growth of ${\mathrm{LaBi}}_2$ with a pristine layer-by-layer growth mode, classifying it as a good metal displaying superconductivity at $\sim 0.55\text{K}$. Compared to ${\mathrm{LaSb}}_2$, we attribute the enhanced metallic behavior and improved growth dynamics of ${\mathrm{LaBi}}_2$ to significant relativistic corrections to its electronic band structure and the resulting impact on both surface energy and intrinsic phonon scattering.

Thermal transport in complex solids is governed by local structure, defects, and anisotropy, yet most continuum models still rely on oversimplified and homogenized conductivities. Here, we bridge atomistic and continuum descriptions by building finite element (FE) models directly from the site-projected thermal conductivity (SPTC), an atomic-level decomposition of the Green–Kubo thermal conductivity. We introduce a toolkit, the “Simulator Collection for Atomic-to-Continuum Scales (SCACS)”, which uses a graph neural network to predict SPTC on large atomic structures, coarse-grains these fields into anisotropic conductivity tensors, and embeds them into the heat-flow FE equation with a customized, anisotropy-aware adaptive mesh refinement scheme. Applied to silicon nanostructures, the resulting FE models act as representative volume elements, reproduce bulk conductivities, and capture interfacial and defect-driven anisotropy while maintaining thermodynamic consistency. Additionally, SCACS predicts experimental conductance trends and fields. This work demonstrates a general route for transferring atomistic transport information into device-scale thermal simulations with physics-based approximations.

We report the synthesis and physical characterization of single-crystalline ${\mathrm{Ce}}_3{\mathrm{MgBi}}_5$, a previously unexplored member of the ${\mathrm{Ce}}_3{MPn}_5$ family. This compound crystallizes in the hexagonal $P{6}_3/mcm$ structure, featuring an anisotropic Ce sublattice composed of zigzag chains along the $c$ axis and a distorted kagome-like network in the basal plane. Magnetization measurements reveal antiferromagnetic order below $T_N\approx 4.2\text{K}$ with strong magnetic anisotropy and multiple field-induced metamagnetic transitions for fields applied perpendicular to [001], leading to a dome-shaped $H–T$ phase diagram. Electrical transport exhibits characteristic signatures of a Ce-based Kondo lattice, including broad resistivity maxima and pronounced field-dependent anomalies in the magnetoresistance and Hall response that track the magnetic phase boundaries. Specific-heat measurements confirm the magnetic transition and show that the full $\text{R}ln2$ entropy expected for a ${\mathrm{Ce}}^{3+}$ Kramers doublet is recovered by 20 K, indicating an extended temperature range of magnetic fluctuations consistent with Kondo correlations. Our results establish ${\mathrm{Ce}}_3{\mathrm{MgBi}}_5$ as a platform within the ${\mathrm{Ce}}_3{MPn}_5$ family for exploring the interplay of geometric frustration, magnetic anisotropy, and Kondo-lattice physics under applied magnetic fields.

Single crystals of $\mathrm{Ag}\mathrm{In}{\mathrm{Cr}}_4{\mathrm{S}}_8$ are grown by chemical vapor transport and crystallographic ordering of Ag/In that results in a breathing pyrochlore motif of ${\mathrm{Cr}}^{3+}$ is verified by x-ray and neutron diffraction. Long-range antiferromagnetic order is observed below a Néel temperature of $T_{\mathrm{N}}$ ≈ 9.6 K. The magnetic properties are characterized using ac and dc magnetization, specific heat capacity, and single crystal neutron diffraction measurements. The specific heat data are characterized by a small lambda anomaly near 9.5 K and the estimated magnetic entropy reaches $\approx$ $\frac{1}{3}$ of the expected value by $3T_{\mathrm{N}}$, suggesting significant short-range order in the paramagnetic phase. Single crystal neutron diffraction evidences an incommensurate spin structure with propagation vector $\mathit{k}=(0,0,\delta )$ and $\delta =0.343$ at 5 K. The minimal model that accounts for the data consists of ferromagnetic layers of Cr atoms, with magnetic moments lying in the plane of the layers and modulating in the perpendicular direction to form a helical structure propagating along $\mathit{k}$. This study represents a rare investigation of single crystals within the family of breathing pyrochlore materials.

Polar orders play a central role in modern technologies, spanning applications from information storage and energy harvesting to neuromorphic computing. While ferroelectric (FE) implementation into devices is more mature, the development of antiferroelectric (AFE)-based devices is still in its infancy. However, AFEs are emerging as promising candidates for multiple applications such as energy storage (supercapacitors), all-solid refrigeration (electrocaloric cooling) or thermal switches. In this work, we probe the transition between the antipolar and polar states in epitaxial layers of the prototypical antiferroelectric oxide, $\mathrm{PbZr}{\mathrm{O}}_3$. We discuss operando second-harmonic generation (SHG) imaging as a powerful tool, providing spatially resolved insights into the electric-field-induced AFE–FE phase transitions. This technique enables the mapping of local symmetry-breaking and phase coexistence during switching, offering a route to unravel the microscopic mechanisms governing AFE–FE transitions in such functional oxides.

The search for intrinsic excitonic insulators (EI) has long been confounded by coexisting electron–phonon coupling in bulk materials. Although the ground state of an EI may be difficult to differentiate from density-wave orders or other structural instabilities, excited states offer distinctive signatures. One way to provide clarity is to directly inspect the phonon spectral function for long wavelength broadening caused by phonon interaction with the high velocity EI phason. Here, we report that the quasi-one-dimensional (quasi-1D) EI candidate ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$ shows extremely anisotropic phonon broadening and softening in the semimetallic normal state. In contrast, such behavior is completely absent in the broken symmetry state of ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$ and in the isostructural ${\mathrm{Ta}}_2{\mathrm{NiS}}_5$ , where the latter has a fully gapped normal state. By contrasting the expected phonon lifetimes in the BCS and BEC limits of a putative EI, our results suggest that the phase transition in ${\mathrm{Ta}}_2\mathrm{Ni}{(\mathrm{Se},\mathrm{S})}_5$ family is closely related to strong interband electron–phonon coupling. We experimentally determine the dimensionless coupling $\frac{g}{{\omega }_0}\sim 10$, revealing ${\mathrm{Ta}}_2\mathrm{Ni}{(\mathrm{Se},\mathrm{S})}_5$ as a rare “ultrastrong coupling” material.

Strong coupling between optical and magnetic excitations could enable contactless, spatially resolved, or ultrafast interrogation and control of magnetism in two-dimensional (2D) materials and devices. The layered 2D A-type antiferromagnet ${\mathrm{CrPS}}_4$ stands out among van der Waals (vdW) magnets for its rich optical fine structure, but its spectroscopy is not yet understood and has so far been interpreted without consideration of magnetic exchange. Here, we show that this fine structure comes primarily from exchange-mediated coupling between on-site optical “spin-flip” transitions of $\mathrm{C}{\mathrm{r}}^{3+}$ and low-energy spin transitions involving the surrounding lattice. Well-resolved magnon sidebands to optical ${}^4\mathrm{A}_2\leftrightarrow {}^2\mathrm{E}$ transitions are observed in photoluminescence (PL) and PL excitation spectra, as well as a pronounced PL sideband associated with short-range exchange splitting. Energy migration is probed using $\mathrm{Y}{\mathrm{b}}^{3+}$ dopants as traps, revealing subpicosecond intersite excitation hopping. Formation of dispersive Frenkel excitons of coupled on-site d-d transitions because of intersite exchange is discussed. In addition to impacting how optical fine structure is interpreted in this and potentially other vdW magnets, these findings may have ramifications for future applications of layered 2D magnets by suggesting potential routes to drive mode-specific spin-wave excitations using light.

We present a comprehensive investigation of reconstructions on $\beta {\text{-Ga}}_2{\mathrm{O}}_3\left(001\right)$ combining first-principles calculations with experimental observations. Using ab initio atomistic thermodynamics and replica-exchange grand-canonical molecular dynamics simulations, we explore the configurational space of possible reconstructions under varying chemical potentials of oxygen and gallium. Our calculations reveal several stable surface reconstructions, most notably a previously unreported $1\times 2$ reconstruction consisting of paired ${\mathrm{GaO}}_4$ tetrahedra that exhibits remarkable stability across a wide range of experimental growth conditions. In this reconstruction, two Ga atoms share one oxygen bond and are separated by a distance of $2.64\AA$ along the [010] direction. High-angle annular dark-field scanning transmission electron microscopy imaging of homoepitaxially grown (001) layers is consistent with the predicted structure. Additional investigations of possible indium substitution at the surface sites, which can occur during indium-mediated metal-exchange catalysis via molecular beam epitaxial growth, reveal a cooperative effect in In incorporation, with distinct stability regions for In-substituted structures under O-rich conditions. Our findings provide an understanding for controlling surface properties during epitaxial growth of $\beta {\text{-Ga}}_2{\mathrm{O}}_3\left(001\right)$.

The emergence of hexagonal Ge (2H-Ge) as a candidate direct-gap group-IV semiconductor for Si photonics mandates a rigorous understanding of its optoelectronic properties. Theoretical predictions of a “pseudodirect” band gap, characterized by weak oscillator strength, contrast with a claimed high radiative recombination coefficient $B$ comparable to conventional (cubic) InAs. We compute $B$ in 2H-Ge from first principles and quantify its dependence on temperature, carrier density, and strain. For unstrained 2H-Ge, our calculated spontaneous emission spectra corroborate that measured photoluminescence corresponds to direct-gap emission, but with $B$ being approximately three orders of magnitude lower than in InAs. We confirm a pseudodirect-to-direct-gap transition under $\sim 2\%$ [0001] uniaxial tension, which can enhance $B$ by up to 3 orders of magnitude, making it comparable to that of InAs. Beyond quantifying the strong enhancement of $B$ via strain engineering, our analysis suggests the dominance of additional, as-yet unquantified recombination mechanisms in this nascent material.

The antiferromagnets with the time-reversal symmetry broken magnetic structures possess a finite spin splitting in the momentum space, and may contribute to a realization of a finite tunnel magnetoresistance (TMR) effect even with magnets with zero net spin polarization. In this paper, we study the TMR effect with the noncollinear antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$ whose inverse ${120}^{\circ }$ antiferromagnetic order breaks the time-reversal symmetry. In particular, we employ the representative barrier material $\mathrm{MgO}$ as the tunnel insulator, and calculate the TMR effect in the ${\mathrm{Mn}}_3\mathrm{Sn}\left(01\overline{1}0\right)/\mathrm{MgO}\left(110\right)/{\mathrm{Mn}}_3\mathrm{Sn}$ magnetic tunnel junctions (MTJs), which has an optimal geometry for the spin-orbit torque switching of the magnetic configurations. We show that a finite TMR ratio reaching $\gtrsim 1000\%$ appears in the ${\mathrm{Mn}}_3\mathrm{Sn}/\mathrm{MgO}/{\mathrm{Mn}}_3\mathrm{Sn}$ MTJs, which is due to the spin splitting properties of ${\mathrm{Mn}}_3\mathrm{Sn}$ in the momentum space combined with the screening effect of $\mathrm{MgO}$.

We report bulk magnetic properties of the monoclinic lanthanide tantalates, $M^{\prime }\text{−}Ln{\mathrm{TaO}}_4$ ($Ln$= Tb, Dy, Ho, Er), where the magnetic $L{n}^{3+}$ ions are arranged on a distorted 2D square lattice. The heavier analog $M^{\prime }\text{−}{\mathrm{YbTaO}}_4$ has been investigated as a spin-orbit-coupled, quasi-two-dimensional frustrated magnet, and the properties of the other $M^{\prime }\text{−}Ln{\mathrm{TaO}}_4$ are expected to vary depending on the electronic configuration of the $Ln$ ion, namely, Kramers vs non-Kramers behavior and different crystal electric field parameters. In this work, powder neutron diffraction is used to confirm the crystal structure for $Ln=$ Tb, Ho, Er, and to determine the magnetic structure of $M^{\prime }\text{−}{\mathrm{TbTaO}}_4$, which displays long-range antiferromagnetic (AFM) order below $T_{\mathrm{N}}=2.1\mathrm{K}$. The ${\mathrm{Tb}}^{3+}$ moments are aligned primarily along the $c$ axis with AFM nearest-neighbor interactions. Susceptibility data suggest that $M^{\prime }\text{−}{\mathrm{DyTaO}}_4$ may display short-range ordering around 2.7 K, while $M^{\prime }\text{−}{\mathrm{HoTaO}}_4$ and $M^{\prime }\text{−}{\mathrm{ErTaO}}_4$ show AFM correlations but do not order above 1.8 K. Measurements of the magnetic specific heat provide evidence for a Kramers doublet ground state in $M^{\prime }\text{−}{\mathrm{ErTaO}}_4$, similar to its heavier analog $M^{\prime }\text{−}{\mathrm{YbTaO}}_4$.

Dielectric particles of the same material exchange electrical charge during collisions or sliding contacts, yet the underlying charge-exchange mechanism is still not understood. The fact that particles can become highly charged as a result of this effect has significant consequences for many settings, both in nature and industry, such as thunderstorms, volcanic eruptions, particle aggregation during meteorite and planet formation, and the clogging of industrial granular systems. Toward understanding these systems, great efforts have been made to develop precise in situ measurements for particle charge, e.g., to determine ensemble charge distributions or measure exchange during individual contacts. Here, we present experimental results concerning the particle size scaling of the stationary-state charge distributions of oxide particles in the sub-millimeter range. We measure the charge distributions for large ensembles of monodisperse ${\mathrm{ZrO}}_2$:${\mathrm{SiO}}_2$ composite spheres, ranging from 172 to $545\mathrm{\mu }\mathrm{m}$ in diameter. These distributions are non-Gaussian and collapse to a single master curve when plotted as functions of the surface charge density $\mathrm{\Sigma }=q/4\pi R^2$. X-ray fluorescence and atomic force microscopy measurements show that the differences in the measured charge distributions are not due to variations in chemical composition or surface roughness, but rather to size alone. Our findings provide constraints on microscopic models for charge exchange, namely that they should lead to steady-state distributions that are non-Gaussian and scale in a specific way with particle size.

Colloidal gels form through the sol-gel transition of attractive particle suspensions, where local aggregation leads to a space-spanning network with solidlike properties. Their microstructure and mechanical properties are highly sensitive to external perturbations, which can substantially alter the pathway of network formation. Here, we investigate how nonlinear oscillatory shear affects the sol-gel transition of colloidal silica suspensions. Using large-amplitude oscillatory shear (LAOS), we vary both the strain amplitude and the duration of oscillatory forcing, varying between one and two times the gelation time. We find that sufficiently large strain amplitudes or prolonged exposure to oscillations in the nonlinear regime irreversibly alter the gel properties: The storage modulus $G^{\prime }$ decreases while its frequency dependence remains unchanged. In contrast, the loss modulus $G^{″}$, which decreases monotonically with frequency under quiescent gelation, exhibits an upturn at high frequencies when the gel is formed under strong oscillatory shear. The viscoelastic spectra of gels formed under quiescent conditions are well captured by a fractional Maxwell model, while gels formed under LAOS require an additional fractional element to account for damage-induced dissipation. Rheo-imaging experiments corroborate this interpretation by revealing the growth of cracks in gels formed under LAOS. We further show that these gels display a progressively more ductile nonlinear response for prolonged exposure to LAOS during gelation. These results demonstrate that the interplay between nonlinear shear and gelation can permanently imprint a macroscopic fracture pattern into colloidal gels, offering a route to tune their viscoelastic properties.